 The pleuronicidae, or flatfish, are remarkable for their asymmetrical bodies. They rest on one side, in the greater number of species on the left, but in some on the right side, and occasionally reversed adult specimens occur. The lower, or resting, surface resembles, at first sight, the ventral surface of an ordinary fish. It is of white color, less developed in many ways than on the upper side, with the lateral fins often of smaller size. But the eyes offer the most remarkable peculiarity, for they are both placed on the upper side of the head. During early youth, however, they stand opposite to each other, and the whole body is then symmetrical, with both sides equally colored. Soon the eye proper to the lower side begins to glide slowly round the head to the upper side, but does not pass right through the skull, as was formerly thought to be the case. It is obvious that, unless the lower eye did this travel round, it could not be used by the fish while lying in its habitual position on one side. The lower eye would also have been liable to be abraded by the sandy bottom. That the pleuronicidae are remarkably adapted by their flattened and asymmetrical structure for their habits of life is manifest from several species, such as souls, flounder, etc., being excessively common. The chief advantages, thus gained, seem to be protection from their enemies and facility for feeding on the ground. The different members, however, of the family present as shiote remarks a long series of forms exhibiting a gradual transition, from hippoglossus pingus, which does not in any considerable degree alter the shape in which it leaves the ovum, to the souls, which are entirely thrown off to one side. Mr. Minvart has taken up this case, and remarks that a sudden spontaneous transformation in the position of the eyes is hardly conceivable, in which I quite agree with him. He then adds, if the transit were gradual, then how such transit of one eye of a minute fraction of the journey toward the other side of the head could benefit the individual is indeed far from clear. It seems even that such an incipient transformation must rather have been injurious. But he might have found an answer to his objection in the excellent observations published in 1867 by Malm. The Plurinesidae, while very young and still symmetrical, with their eyes standing on opposite sides of the head, cannot long retain a vertical position owing to the excessive depth of their bodies, the small size of their lateral fins, and to their being destitute of a swim bladder. Hence soon growing tired, they fall to the bottom, on one side. While thus at rest they often twist as Malm observed the lower eye upward to see above them, and they do so so vigorously that the eye is pressed hard against the upper part of the orbit. The forehead between the eyes consequently becomes, as could plainly be seen, temporarily contracted in breadth. On one occasion Malm saw a young fish raise and depress the lower eye through an angular distance of about seventy degrees. We should remember that the skull at this early age is cartilaginous and flexible, and so it readily yields to muscular action. It is also known, with the higher animals, even after early youth, that the skull yields and is altered in shape, if the skin or muscles be permanently contracted through diseases or some accident. With long-eared rabbits, if one ear flops forward and downward, its weight drags forward all the bones of the skull on the same side, of which I have given a figure. Malm states that the newly hatched young of perches, salmon, and several other symmetrical fishes, have the habit of occasionally resting on one side at the bottom, and he has observed that they often then strain their lower eyes so as to look upward, and their skulls are thus rendered rather crooked. These fishes, however, are soon able to hold themselves in a vertical position, and no permanent effect is thus produced. With the pleuricidae, on the other hand, the older they grow, the more habitually they rest on one side, owing to the increasing flatness of their bodies, and a permanent effect is thus produced at the form of the head, and on the position of the eyes. Judging from analogy, the tendency to distortion would no doubt be increased through the principle of inheritance. Schoete believes, in opposition to some other naturalists, that the pleuricidae are not quite symmetrical even in the embryo, and if this be so, we could understand how it is that certain species, while young, habitually fall over and rest on the left side, and other species on the right side. Malmads, in confirmation of the above view, that the adult tracheopterus arcturus, which is not a member of the pleuricidae today, rests on the left side at the bottom, and swims diagonally through the water, and this fish of the two sides of its head are said to be somewhat dissimilar. Our great authority on fishes, Dr. Gunther, concludes his abstract of Malm's paper by remarking that the author gives a very simple explanation of the abnormal condition of the pleuricentinoids. We thus see that the first stages of the transit of the eye from one side of the head to the other, which Mr. Minvart considers would be injurious, may be attributed to the habit, no doubt beneficial to the individual and to the species, of endeavoring to look upward with both eyes, while resting on one side at the bottom. We may also attribute to the inherited effects of use the fact of the mouth in several kinds of flatfish being bent toward the lower surface, with the jawbones stronger and more effective on this, the eyeless side of the head, than on the other, for the sake, as Dr. Tranquayar supposes, of feeding with ease on the ground. Disuse, on the other hand, will account for less developed conditions of the whole inferior half of the body, including the lateral fins, though Yarel thinks that the reduced size of these fins is advantageous to the fish, as there is so much less room for the action than with the larger fins above. Perhaps the lesser number of teeth than the proportion of four to seven in the upper halves of the two jaws of the pliase to twenty-five to thirty in the lower halves, may likewise be accounted for by disuse. From the colorless state of the ventral surface of many fishes, and from many other animals, we may reasonably suppose that the absence of color in flatfish on the side, whether it be right or left, which is undermost, is due to the exclusion of light, but it cannot be supposed that the peculiar speckled appearance of the upper side of the soul is so like the sandy bed of the sea, or the power in some species, as recently shown by Pouché, of changing their color in accordance with the surrounding surface, or the presence of bony tubercles in the upper side of the turbo, are due to the action of the light. Here natural selection has probably come into play, as well as in adapting the general shape of the body of these fishes, and many other peculiarities to their habits of life. We should keep in mind, as I have before insisted, that the inherited effects of the increased use of parts, and perhaps of their disuse, will be strengthened by natural selection, for all spontaneous variations in the right direction will be thus preserved, as will those individuals which inherit, in the highest degree, the effects of the increased beneficial use of any part. How much to attribute in each particular case to the effects of use, and how much to natural selection, it seems impossible to decide. I may give another instance of a structure which apparently owes its origin exclusively to use, or habit. The extremity of the tail in some American monkeys has been converted into a wonderfully perfect prehensile organ, and serves as a fifth hand. A reviewer, who agrees with Mr. Minvart in every detail, remarks on this structure. It is impossible to believe that in any number of ages the first slight incipient tendency to grass could preserve the lives of the individuals possessing it, or favor their chance of having and of rearing offspring. But there is no necessity for any such belief. Habit, and this almost implies that some benefit of great or small is thus derived, would in all probabilities suffice for the work. Bram saw the young of an African monkey, Cersopithecus, clinging to the under surface of their mother by their hands, and at the same time they hooked their little tails round that of their mother. Professor Henslow kept in confinement some harvest mice, mousse misorias, which do not possess a structurally prehensive tail, but he frequently observed that they curled their tails round the branches of a bush placed in the cage, and thus aided themselves in climbing. I have received an analogous account from Dr. Gunther, who has seen a mouse thus suspend itself. If the harvest mouse had been more strictly arboreal, it would perhaps have had its tail rendered structurally prehensile, as is the case with some members of the same order. Why Cersopithecus, considering its habits while young has not become thus provided, it would be difficult to say. It is, however, possible that the long tail of this monkey may be more of service to it as a balancing organ in making its prodigious leaps than as a prehensile organ. The memory glands are common to the whole class of mammals, and are indispensable for their existence. They must therefore have been developed at an extremely remote period, and we can know nothing positively about their manner of development. Mr. Minvard asks, is it conceivable that the young of any animal was ever saved from destruction by accidentally sucking a drop of scarcely nutritious fluid from an accidentally hypertrophied cutationous gland of its mother, and even if one were so, what chance was there of the perpetuation of such a variation? But the case is not here, put fairly. It is admitted by most evolutionists that mammals are descended from a marsupial form, and if so, the memory glands will have at first developed within the marsupial sac. In the case of fish, hippocampus, the eggs are hatched, and the young are reared for a time within a sac of this nature, and an American naturalist, Mr. Lockwood, believes from what he has seen of the development of the young that they are nourished by a secretion from the coutaneous glands of the sac. Now with the early progenitors of mammals, almost before they deserve to be thus designated, is it not at least possible that the young might have been similarly nourished? And in this case the individuals which secreted a fluid in some degree or manner the most nutritious so as to partake of the nature of milk would in the long run have reared a larger number of well-nourished offspring than would the individuals which secreted a poorer fluid, and thus the coutaneous glands, which are the homologues of the memory glands, would have been improved or rendered more effective. It accords with the widely extended principle of specialization that the glands over a certain space of the sac should have become more highly developed than the remainder, and that they would then have formed a breast, but at first without a nipple, as we see in the ornithorinkus at the base of the mammalian series. Through what agency the glands over a certain space become more highly specialized than the others, I will not pretend to decide, whether in part through compensation of growth, the effects of youth or natural selection. The development of the memory glands would have been of no service and could not have been affected through natural selection unless the young at the same time were able to partake of the secretion. There is no greater difficulty in understanding how young mammals have instinctively learned to suck the breast than in understanding how unhatched chickens have learned to break the eggshell by tapping against it with their specially adapted beaks, or how a few hours after leaving the shell they have learned to pick up grains of food. In such cases the most probable solution seems to be that the habit was at first acquired by a practice at a more advanced age, and afterwards transmitted to the offspring at an earlier age. But the young kangaroo is said not to suck, only to cling to the nipple of its mother, who has the power of injecting milk into the mouth of her helpless half-formed offspring. On this head Mr. Minvart remarks, did no special provision exist? The young one must infallibly be choked up by the intrusion of the milk into the windpipe. But there is a special provision. The larynx is so elongated that it arises up into the posterior end of the nasal passage, and is thus enabled to give free entrance to the air for the lungs, while the milk passes harmlessly on each side of this elongated larynx, and so safely attains the gullet behind it. Mr. Minvart then asks how did natural selection remove in the adult kangaroo, and in most other mammals on the assumption that they are descended from a marsupial form, this at least perfectly innocent and harmless structure? It may be suggested in answer that the voice, which is certainly of high importance to many mammals, could hardly have been used with full force as long as the larynx entered the nasal passage, and Professor Faur has suggested to me that this structure would have greatly interfered with an animal's swallowing solid food. We will now turn for a short space to the lower divisions of the animal kingdom. The Ikainu-dermata, starfishes, sea urchins, etc., are furnished with remarkable organs called pedicelary, which consist when well developed of a tridactyl forceps, that is, of one form of three serrated arms, neatly fitting together and placed on the summit of a flexible stem moved by muscles. These forceps can seize and firmly hold of any object, and Alexander Argeses has seen any kinus or sea urchin rapidly passing particles of excrement from forceps to forceps down certain lines of its body in order that its shell should not be fouled. But there is no doubt that besides removing dirt of all kinds they subserve other functions, and one of these apparently is defense. With respect to these organs, Mr. Minvart, as on so many previous occasions, asks, what would be the utility of the first rudimentary beginnings of such structures, and how could such incipient buddings ever have preserved the life of a single echinus? He adds, not even the sudden development of the snapping action would have been beneficial without the freely movable stalk, nor could the latter have been efficient without the snapping jaws, yet no minute nearly indefinite variations could have simultaneously evolved these complex coordination of structure. To deny this seems to do no less than to affirm a startling paradox. Paradoxical as this may appear to Mr. Minvart, tridactyl forcepses immovably fixed at the base but capable of a snapping action certainly do exist on some starfishes, and this is intelligible if they serve at least in part as a means of defense. Mr. Agassiz, to whose great kindness I am indebted for much information on the subject, informs me that there are other starfishes in which one of the three arms of the forcepses reduced to a support for the other two, and again other genera in which the third arm is completely lost. In Echinosis the shell is described by Monsieur Perrier as bearing two kinds of pediculary, one resembling that of Echinus and the other those of Spatangas, and in such cases are always interesting as affording the means of apparently sudden transitions through the abortion of one of the two states of an organ. With respect to the steps by which these curious organs have evolved, Mr. Agassiz infers from his own researches and those of Mr. Mueller that both in starfishes and sea urchins the pediculary have undoubtedly been looked at as modified spines. This must be inferred from their manner of development in the individual, as well as from a long and perfect series of gradations in different species and genera, from simple granules to ordinary spines to perfect tridactyl pediculary. This gradation extends even to the manner in which ordinary spines and the pediculary, with their supporting calciferous rods, are articulated to the shell. In certain genera of starfishes the very combinations needed to show that the pediculary are only modified branching spines may be found. Thus we have fixed spines with three equidistant serrated movable branches articulated to near their bases and higher up on the same spine three other movable branches. Now when the latter arise from the summit of a spine they form in fact a rude tridactyl pediculary, and as such may be seen on the same spine together with the three lower branches. In this case the identity in nature between the arms of the pediculary and the movable branches of a spine is unmistakable. It is generally admitted that the ordinary spine serve as a protection, and if so there can be no reason to doubt that those furnished with serrated and movable branches likewise serve for the same purpose, and they would thus serve still more effectively as soon as by meeting together they acted as a prehensile or snapping apparatus. Thus every gradation from an ordinary fixed spine to a fixed pediculary would be of service. In certain genera of starfishes these organs instead of being fixed or borne on an immovable support are placed at the summit of a flexible and muscular though short stem, and in this case they probably subserve some additional function besides defense. In the sea urchins the steps can be followed by which a fixed spine becomes articulated to the shell, and is thus rendered movable. I wish I had space here to give a fuller abstract of Mr. Agassi's interesting observations on the development of the pediculary. All possible gradations as he adds may likewise be found between the pediculary of the starfishes and the hooks of the Ophiolarians, another group of the Echinodermata, and again between the pediculary of sea urchins and the anchors of the Holothrae, also belonging to the same great class. Certain compound animals or zoophytes as they have been termed, namely the polyzoa, are provided with curious organs called avicularia. These differ much in structure in the different species. In their most perfect condition they curiously resemble the head and beak of a vulture in miniature, seated on the neck and capable of movement, as is likewise the lower jaw or mandible. In one species observed by me, all the avicularia on the same branch often moved simultaneously backwards and forwards with the lower jaw widely open through an angle of about 90 degrees in the course of five seconds, and their movement caused the whole polyzory to tremble. When the jaws are touched with a needle they seize it so firmly that the branch can thus be shaken. Mr. Minvar deduces this case chiefly on account of the supposed difficulty of organs, namely the avicularia of the polyzoa and the pediculary of the echinodermata, which he considers as essentially similar, having been developed through natural selection in widely distinct divisions of the animal kingdom. But as far as the structure is concerned I can see no similarity between tridactile pediculary and avicularia. The latter resembles somewhat more closely the chile or pincers of crustaceans, and Mr. Minvar might have deduced with equal appropriateness this resemblance has a special difficulty, or even their resemblance to the head and beak of a bird. The avicularia are believed by Mr. Busk, Dr. Smith, and Dr. Nietzsche, naturalists who have carefully studied this group, to be homologous with the zoids and their cells which composite the zoophyte. The movable lip or lid of the cell corresponding with the lower and movable mandible of the avicularium. Mr. Busk, however, does not know of any gradations now existing between a zooid and an avicularium. It is therefore impossible to conjecture by wet, serviceable gradations the one could have been converted into the other, but it by no means follows from this that such gradations have not existed. As the chile of crustaceans resemble in some degree the avicularia of Pollyzoa, both serving as pincers, it may be worthwhile to show that with the former, a long series of serviceable gradations still exists. In the first and simplest stage, the terminal segment of the limb shuts down either on the square summit of the broad penultimate segment or against the whole side and is thus unable to catch hold of an object, but the limb still serves as an organ of locomotion. We next find one corner of the broad penultimate segment slightly prominent, sometimes furnished with irregular teeth and against these the terminal segment shuts down, but an increase in the size of this projection with its shape as well as that of the terminal segment slightly modified and improved, the pincers are rendered more and more perfect until at last we have an instrument as efficient as the chile of a lobster and all these gradations can actually be traced. Besides the avicularia, the Pollyzoa possess curious organs called the brocula. These generally consist of long bristles capable of movement and easily excited. In one species examined by me, the brocula were slightly curved and serrated along the outer margin and all of them on the same Pollyzoa often moved simultaneously so that acting like long oars, they swept a branch rapidly across the object glass of my microscope. When a branch was placed on the face, the brocula became entangled and they made violent efforts to free themselves. They are supposed to serve as a defense and may be seen as Mr. Bust remarks to sweep slowly and carefully over the surface of the Pollyzoa removing what might be noxious to the delicate inhabitants of the cells when their tentacular are protruded. The avicularia, like the vibrocula, probably serve for defense, but they also catch and kill small living animals which it is believed are afterwards swept by the currents within the reach of the tentacular of the zoids. Some species are provided with avicularia and vibrocula, some with avicularia alone and a few with vibrocula alone. It is not easy to imagine two objects more widely different in appearance than a bristle or a vibraculum and an avicularium like the head of a bird, yet they are almost certainly homologous and have been developed from the same common source, namely a zoid with its cell. Hence we can understand how it is that these organs greatate in some cases as I am informed by Mr. Bust into each other. Thus with the avicularia of some species of lepralia the movable mandible is so much produced and is so like that of a bristle that the presence of the upper or fixed beak alone serves to determine its avicularia nature. The vibracula may have been directly developed from the lips of the cells without having passed through the avicularia stage but it seems more probable that they have passed through this stage as during the early stages of the transformation the other parts of the cell with the included zoid could hardly have disappeared at once. In many cases the vibracula have a grooved support at the base which seems to represent the fixed beak though the support in some species is quite absent. This view of the development of the vibracula if trustworthy is interesting for supposing that all the species provided with avicularia had become extinct no one with the most vivid imagination would ever have thought that the vibracula had originally existed as a part of an organ resembling a bird's head or an irregular box or hood. It is interesting to see two such widely different organs developed from a common origin and as the movable lip of the cell serves as a protection of the zoid there is no difficulty in believing that all the gradations by which the lip became converted first into the lower mandible of an avicularium and then into an elongated bristle likewise served as a protection in different ways and under different circumstances. In the vegetable kingdom Mr. Minvart only alludes to two cases namely the structure of the flowers of orchids and the movements of climbing plants. With respect to the former he says the explanation of their origin is deemed thoroughly unsatisfactory utterly insufficient to explain the incipient infinitesimal beginnings of structures which are of utility only when they are considerably developed. As I have fully treated this subject in another work I will here give only a few details on one alone of the most striking peculiarities of the flowers of orchids namely their polinia. A polinum when highly developed consists of a mass of pollen grains affixed to an elastic footstock or cortical and this to a little mass of extremely viscid matter. The polinia are by this means transported by insects from one flower to the stigma of another. In some orchids there is no cortical to the pollen masses and the grains are merely tied together by fine threads but as these are not confined to orchids they need not here be considered. Yet I may mention that at the base of the Orcanidus series in cyberspatium we can see how the threads were probably first developed. In other orchids the threads cohere at one end of the pollen masses and this forms the first or nascent trace of a clotical. This is the origin of the clotical even when of considerable length and highly developed we have good evidence in the aborted pollen grains which can sometimes be detected embedded within the central and solid parts. With respect to the second chief peculiarity namely the little mass of viscid matter attached to the end of the clotical a long series of gradations can be specified each of plain service to the plant. In most flowers belonging to other orders the stigma secretes a little viscid matter. Now in certain orchids similar viscid matter is secreted but in much larger quantities by one alone of the three stigmas and this stigma perhaps in consequence of the copious secretion is rendered sterile. When an insect visits a flower of this kind it rubs off some of the viscid matter and thus at the same time drags away some of the pollen grains. From this simple condition which differs but little from that of a multitude of common flowers there are endless gradations to species in which the pollen mass terminates in a very short free clotical to others in which the clotical becomes firmly attached to the viscid matter which the sterile stigmata itself much modified. In this latter case we have a polinium in its most highly developed and perfect condition. He who will carefully examine the flowers of orchids for himself will not deny the existence of the above series of gradations. From a mass of pollen grains merely tied together by threads with the stigmata differing but little from that of the ordinary flowers to a highly complex polinium admirably adapted for transportal by insects. Nor will he deny that all the gradations and the several species are admirably adapted in relation to the general structure of each flower for its fertilization by different insects. In this and almost every other case the inquiry must be pushed further backwards and it must be asked how did the stigma of an ordinary flower become viscid? But as we do not know the full history of any one group of beings it is as useless to ask as it is hopeless to attempt answering such questions. We will now turn to climbing plants. These can be arranged in a long series from those which simply twine round the support to those which I have called leaf climbers and to those provided with tendrils. In these two latter cases the stems have generally but not always lost the power of twining though they retain the power of revolving which the tendrils likewise possess. The gradations from leaf climbers to tendril bearers are wonderfully close and certain plants may be differently placed in either class. But in ascending the series from simple twiners to leaf climbers an important quality is added namely sensitiveness to a touch by means of the footstocks of the leaves of the flowers or these modified and converted into tendrils or excited to bend round and clasp the touching object. He who will read my memoir on these plants will I think admit that all the gradations in function and structure between simple twiners and tendril bearers are in each case beneficial in a high degree to the species. For instance it is clearly a great advantage to a twining plant to become a leaf climber and it is probable that every twiner which possessed leaves with long footstocks would have been developed into a leaf climber if the footstocks had possessed in any slight degree the requisite sensitiveness to a touch. As twining is the simplest means of ascending a support and forms the basis of our series it may naturally be asked how did plants acquire this power in an incipient degree? Afterwards to be improved and increased through natural selection. The power of twining depends firstly on the stems while young being extremely flexible but this is a character common to many plants which are not climbers and secondly on their continually bending to all points of the compass one after another in succession in the same order. By this movement the stems are inclined to all sides and are made to move round and round. As soon as the lower part of a stem strikes against any object and is stopped the upper part still goes on bending and revolving and thus necessarily twines round and up the support. The revolving movement ceases after the early growth of each shoot as in many widely separated families of plants single species and single genera possess the power of revolving and have thus become twiners. They must have independently acquired it and cannot have inherited it from a common progenitor. Hence I was led to predict that some slight tendency to a movement of this kind would be found to be far from uncommon with plants which did not climb and that this had afforded the basis for natural selection to work on and improve. When I made this prediction I knew of only one imperfect case namely of the young flower pendicles of a moronda which revolved slightly and irregularly like the stems of trining plants but without making any use of this habit. Soon afterwards Fritz Muller discovered that the young stems of alisma and of a lenom plants which do not climb and are widely separated in the natural system revolved plainly though irregularly and he states that he has reason to suspect that this occurs with some other plants. These slight movements appear to be of no service to the plants in question. Anyhow they are not of the least use in the way of climbing which is the point that concerns us. Nevertheless we can see that if the stems of these plants had been flexible and if under the conditions to which they are exposed it had profited them to ascend to a height then the habit of unsightly and irregularly revolving might have been increased and utilized through natural selection until they had become converted into well-developed twining species. With respect to the sensitiveness of the footstocks of the leaves and flowers and of the tendrils nearly the same remarks are applicable as in the case of the revolving movements of twining plants. As a vast number of species belonging to widely distinct groups are endowed with this kind of sensitiveness it ought to be found in a nascent condition in many plants which have not become climbers. This is the case. I observed that the young flower pentacles of the above Morandia curved themselves a little towards the side which was touched. Moran found in several species of oxalis that the leaves and their footstocks moved especially after exposure to a hot sun when they were gently and repeatedly touched or when the plant was shaken. I repeated these observations on some other species of oxalis with the same result. In some of them the movement was distinct but was best seen in the young leaves. In others it was extremely slight but it is a more important fact that according to the high authority of Hofmeister the young shoots and leaves of all plants move after being shaken and with climbing plants it is as we know only during the early stages of growth that the footstocks and tendrils are sensitive. It is scarcely possible that the above slight movements due to a touch or shake in the young and growing organs of plants can be of any functional importance to them. But plants possess in obedience to various stimuli powers of movement which are of manifest importance to them. For instance, towards and more rarely from the light in opposition to and more rarely in the direction of the attraction of gravity when the nerves and muscles of an animal are excited by galvanism or by the absorption of strict nine the consequent movements may be called an incidental result for the nerves and muscles have not been rendered specially sensitive to these stimuli. So with plants it appears that from having the power of movement in obedience to certain stimuli they are excited in an incidental manner by a touch or by being shaken. Hence there is no great difficulty in admitting that in the case of leaf climbers and tendril bearers it is this tendency which has been taken advantage of and increased through natural selection. It is however probable from reasons which I have assigned in my memoir that this will have occurred only with plants which had already acquired the power of revolving and had thus become twiners. I have already endeavored to explain how plants become twiners namely by the increase of a tendency to slight and irregular revolving movements which were at first of no use to them. This movement as well as that due to a touch or a shake being the incidental result of the power of moving gained for other and beneficial purposes. Whether during the gradual development of climbing plants natural selection has been aided by the inherent effects of use I will not pretend to decide but we know that certain periodical movements for instance the so-called sleep of plants are governed by habit. I have now considered enough perhaps more than enough of the cases selected with care by a skillful naturalist to prove that natural selection is incompetent to account for the incipient changes of useful structures. And I have shown as I hope that there is no great difficulty on this head. A good opportunity has thus been afforded for enlarging a little on gradations of structure often associated with strange functions, an important subject which was not treated at sufficient length in former additions of this work. I will now briefly recapitulate the foregoing cases. With the giraffe, the continued preservation of the individuals of some extinct high-reaching ruminant which had the longest necks, legs, et cetera, and could browse a little above the average height and the continued destruction of those who could not browse so high would have sufficed for the production of this remarkable quadruped. But the prolonged use of all the parts together with inheritance will have aided in an important manner in their coordination. With the many insects which imitate various objects there is no improbability in the belief that an accidental resemblance to some common object was in each case the foundation for the preservation of slight variations which made the resemblance at all closer. And this will have been carried on as long as the insect continued to vary and as long as a more and more perfect resemblance led to its escape from sharp-sighted enemies. In certain species of whales there is a tendency to the formation of irregular little points of horn on the palate and it seems to be quite within the scope of natural selection to preserve all favorable variations until the points were converted first into laminated knobs or teeth like those on the beak of a goose, then into short lamellae like those of the domestic ducks and then into lamellae as perfect as those of the shoveler duck. And finally into the gigantic plates of baleen as in the mouth of the Greenland Whale. In the family of these ducks the lamellae are first used as teeth, then partly as teeth, then partly as a sifting apparatus and at last almost exclusively for this latter purpose. With such structures as the above lamellae of horn or whale bone, habit or use can have done little or nothing as far as we can judge toward their development. On the other hand the transportal of the lower eye of a flat fish to the upper side of the head and the formation of a prehensile tail may be attributed almost wholly to continued use together with inheritance. With respect to the mammae of the higher animals the most probable conjecture is that primordially the cutaneous glands over the whole surface of the marsupial sac secreted a nutritious fluid and that these glands were improved in function through natural selection and concentrated into a confined area in which case they would have formed a mammae. There is no more difficulty in understanding how the branched spines of some ancient Echinoderm which served as a defense became developed through natural selection into tritactyl pediculiae than in understanding the development of the pincers of crustaceans through slight serviceable modifications in the ultimate and penultimate segments of a limb which was at first used solely for locomotion. In the aviculariae and vibraculae of the polyzoa we have organs widely different in appearance developed from the same source and with the vibraculae we can understand how the successive gradations might have been of service. With the poliniae of orchids the threads which originally served to tie together the pollen grains can be traced cohering into corticles and these steps can likewise be followed by which viscid matter such as that secreted by the stigmas of ordinary flowers and still subserving nearly but not quite the same purpose became attached to the free ends of the corticles. All these gradations being of manifest benefit to the plants in question. With respect to climbing plants I need not repeat what has been so lately said. It has often been asked if natural selection be so potent why has not this or that structure been gained by certain species to which it would apparently have been advantageous. But it is unreasonable to expect a precise answer to such questions considering our ignorance of the past history of each species and of the conditions which at the present day determine its numbers and range. In most cases only general reasons but in some few cases special reasons can be assigned. Thus to adapt a species to new habits of life many coordinated modifications are almost indispensable and it may often have happened that the requisite parts did not vary in the right manner or to the right degree. Many species must have been prevented from increasing in numbers through destructive agencies which stood in no relation to certain structures which we imagine would have been gained through natural selection from appearing to us advantageous to the species. In this case as the struggle for life did not depend on such structures they could not have been acquired through natural selection. In many cases complex and long enduring conditions often of the peculiar nature are necessary for the development of a structure and the requisite conditions may seldom have concurred. The belief that any given structure which we think often erroneously would have been beneficial to a species would have been gained under all circumstances through natural selection. It is opposed to what we can understand of its manner of action. Mr. Minbart does not deny that natural selection has affected something but he considers it as demonstrably insufficient to account for the phenomenon which I explained by its agency. His chief arguments have now been considered and the others will hereafter be considered. They seem to me to partake little of the character of demonstration and to have little weight in comparison with those in favor of the power of natural selection aided by the other agencies often specified. I am bound to add that some of the facts and arguments here used by me have been advanced for the same purpose in an ABLE article lately published in the Medical Chaiological Review. At the present day almost all naturalists admit evolution under some form. Mr. Minbart believes that species changed through an internal force or tendency about which it is not pretended that anything is known. That species have the capacity for change will be admitted by all evolutionists but there is no need as it seems to me to invoke any internal force beyond the tendency to ordinary variability which through the aid of selection by man has given rise to many well adapted domestic races and which through the aid of natural selection would equally well give rise by graduated steps to natural races or species. The final result will generally have been as already explained in advance but in some few cases a retrogression, an organization. Mr. Minbart is further inclined to believe and some naturalists agree with him that new species manifest themselves with suddenness and by modifications appearing at once. For instance, he supposes that the differences between the extinct three-toed Hipparian and the horse arose suddenly. He thinks it difficult to believe that the wing of a bird was developed in any other way than by a completely sudden modification of a marked and important kind and apparently he would extend the same view to the wings of bats and productiles. This conclusion which implies great breaks of discontinuity in the series appears to me improbable in the highest degree. Everyone who believes in slow and gradual evolution will of course admit that specific changes may have been as abrupt and as great as any single variation which we meet with under nature or even under domestication. But as species are more variable when domesticated or cultivated than under their natural conditions it is not probable that such great and abrupt variations have often occurred under nature as are known occasionally to arise under domestication. Of these latter variations several may be attributed to reversion and the characters which thus reappear were it is probable in many cases at first gained in a gradual manner. A still greater number must be called monstrosities such as six-fingered men, porcupine men, ancon sheep, neata cattle, et cetera. And as they are widely different in character from natural species they throw very little light on our subject. Excluding such cases of abrupt variations the few which remain would at best constitute if found in a state of nature doubtful species closely related to their parental types. My reasons for doubting whether natural species have changed as abruptly as have occasionally domestic races and for entirely disbelieving that they have changed in the wonderful manner indicated by Mr. Minvart are as follows. According to our experience abrupt and strongly marked variations occur in our domesticated productions singly and at rather long intervals of time. If such occurred under nature they would be liable as formerly explained to be lost by accidental causes of destruction and by subsequent intercrossing. And so it is known to be under domestication unless abrupt variations of this kind are specially preserved and separated by the care of man. Hence in order that a new species should suddenly appear in the manner supposed by Mr. Minvart it is almost necessary to believe in opposition to all analogy that several wonderfully changed individuals appeared simultaneously within the same district. This difficulty as in the case of unconscious selection by man is avoided on the theory of gradual evolution through the preservation of a large number of individuals which varied more or less in any favorable direction and of the destruction of a large number which varied in the opposite manner. That many species have been evolved in an extremely gradual manner there can hardly be a doubt. The species and even the genera of many large natural families are so closely allied together that it is difficult to distinguish not a few of them. On every continent in proceeding from north to south from lowland to upland, et cetera we meet with a host of closely related or representative species as we are likely to do on certain distinct continents which we have reason to believe were formerly connected. But in making these and the following remarks I am compelled to allude to subjects here and after to be discussed. Look at the many outlying islands round a continent and see how many of their inhabitants can be raised only to the rank of doubtful species. So it is that if we look to past times and compare the species which have just passed away with those still living within the same areas or if we compare the fossil species embedded in the substages of the same geological formation it is indeed manifest that multitudes of species are related in the closest manner to other species that still exists or have lately existed and it will hardly be maintained that such species have been developed in an abrupt or sudden manner. Nor should it be forgotten when we look to the special parts of allied species instead of two distinct species that numerous and wonderfully fine gradations can be traced connecting together widely different structures. Many large groups of facts are intelligible only on the principle that species have been evolved by very small steps. For instance, the fact that the species included in the larger genera are more closely related to each other and present a greater number of varieties than do the species in the smaller genera. The former are also grouped in little clusters like varieties around species and they present other analogies with varieties as was shown in our second chapter. On this same principle, we can understand how it is that specific characters are more variable than generic characters and how the parts which are developed in an extraordinary degree or manner are more variable than other parts of the same species. Many analogous facts all pointing in the same direction could be added. Although many species have almost certainly been produced by steps not greater than those separating fine varieties, yet it may be maintained that some have been developed in a different and abrupt manner. Such an admission, however, ought not to be made without strong evidence being assigned. The vague and in some respects false analogies as they have been shown to be by Mr. Chauncey Wright which have been advanced in favor of this view such as the sudden crystallization of inorganic substances or the falling of a faceted spheroid from one facet to another, hardly deserve consideration. One class of facts, however, namely the sudden appearance of new and distinct forms of life in our geological formations, supports at first sight the belief in abrupt development. But the value of this evidence depends almost entirely on the perfection of the geological record in relation to periods remote in the history of the world. If the record is as fragmentary as many geologists strenuously assert, there is nothing strange in new forms appearing as if suddenly developed. Unless we admit transformations as prodigious as those advocated by Mr. Minbart, such as the sudden development of the wings of birds or bats or the sudden conversion of a hyperion into a horse, hardly any light is thrown by the belief in abrupt modifications on the deficiency of connecting links in our geological formations. But against the belief in such abrupt changes, embryology enters a strong protest. It is notorious that the wings of bats and birds and the legs of horses or other quadrupeds are indistinguishable at an early embryonic period and they become differentiated by insensibly fine steps. Embryological resemblances of all kinds can be accounted for as we shall hear after see by the progenitors of our existing species having buried after early youth and having transmitted their newly acquired characters to their offspring at a corresponding age. The embryo is thus left almost unaffected and serves as a record of the past condition of the species. Hence it is that existing species during the early stages of their development so often resemble ancient and extinct forms belonging to the same class. On this view of the meaning of embryological resemblances and indeed on any view it is incredible that an animal should have undergone such momentous and abrupt transformations as those above indicated and yet should not bear even a trace in its embryonic condition of any sudden modification, every detail in its structure being developed by insensibly fine steps. He who believes that some ancient form was transformed suddenly through an internal force or tendency into for instance one furnished with wings will be almost compelled to assume in opposition to all analogy that many individuals varied simultaneously. It cannot be denied that such abrupt and great changes of structure are widely different from those which most species apparently have undergone. He will further be compelled to believe that many structures beautifully adapted to all the other parts of the same creature and to the surrounding conditions have been suddenly produced and of such complex and wonderful co-adaptations he will not be able to assign a shadow of an explanation. He will be forced to admit that these great and sudden transformations have left no trace of their action on the embryo. To admit all this is as it seems to me to enter into the realms of miracle and to leave those of science. So ends chapter seven, miscellaneous objections to the theory of natural selection. This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. Recorded by Gesina. The origin of species by means of natural selection or the preservation of favored races in the struggle for life. Six London Edition by Charles Darwin. Chapter eight, part one. Instinct, contents of this chapter include instincts comparable with habits but different in their origin, instincts graduated, affidies and ants, instincts variable, domestic instincts, their origin, natural instincts of the cuckoo, molluscus, ostrich and parasitic bees, slave making ants, hive bee, its cell making instinct, changes of instinct and structure not necessarily simultaneous, difficulties of the theory of natural selection of instincts, neuter or sterile insects, summary. Many instincts are so wonderful that their development will probably appear to the reader a difficulty sufficient to overthrow my whole theory. I may hear premise that I have nothing to do with the origin of the mental powers any more than a half with that of life itself. We are concerned only with the diversities of instinct and of the other mental faculties and animals of the same class. I will not attempt any definition of instinct. It would be easy to show that several distinct mental actions are commonly embraced by this term but everyone understands what is meant when it is said that instinct impels the cuckoo to migrate and to lay her eggs in other bird's nests. An action which we ourselves require experience to enable us to perform when performed by an animal, more especially by a very young one, without experience, and when performed by many individuals in the same way without their knowing for what purpose it is performed is usually said to be instinctive. But I could show that none of these characters are universal. A little dose of judgment or reason as Pierre Huber expresses it often comes into play even with animals low in the scale of nature. Frederick Cuivier and several of the older metaphysicians have compared instinct with habit. This comparison gives, I think, an accurate notion of the frame of mind under which an instinctive action is performed but not necessarily of its origin. How unconsciously many habitual actions are performed, indeed not rarely in direct opposition of our conscious will. Yet they may be modified by the will or reason. Habits easily become associated with other habits with certain periods of time and states of the body. When once acquired, they often remain constant throughout life. Several other points of resemblance between instinct and habits could be pointed out. As in repeating a well-known song, so in instincts, one action follows another by a sort of rhythm. If a person be interrupted in a song or in repeating anything by rote, he is generally forced to go back to recover the habitual train of thought. So Pierre Huber found it was with a caterpillar which makes a very complicated hammock. For if he took a caterpillar which had completed its hammock up to, say, the sixth stage of construction and put it into a hammock completed only the third stage, the caterpillar simply re-performed the fourth, fifth and sixth stages of construction. If, however, a caterpillar were taken out of a hammock made up, for instance, to the third stage and were put into one finished up to the sixth stage so that much of its work was already done for it, far from deriving any benefit from this, it was much embarrassed and, in order to complete its hammock, seemed forced to start from the third stage where it had left off and thus tried to complete the already finished work. If we suppose any habitual action to become inherited and it can be shown that this does sometimes happen, then the resemblance between what originally was a habit and an instinct becomes so close as not to be distinguished. If Mozart, instead of playing the piano forte at three years old with wonderfully little practice, had played a tune with no practice at all, he might truly be said to have done so instinctively. But it would be a serious error to suppose that the greater number of instincts have been acquired by habit in one generation and then transmitted by inheritance to succeeding generations. It can be clearly shown that the most wonderful instincts with which we are acquainted, namely those of the hive bee and of many ants, could not possibly have been acquired by habit. It will be universally admitted that instincts are as important as corporeal structures for the welfare of each species under its present conditions of life. Under changed conditions of life, it is at least possible that slight modifications of instinct may be profitable to a species and if it can be shown that instincts do vary ever so little, then I can see no difficulty in natural selection preserving and continually accumulating variations of instinct to any extent that was profitable. It is thus, as I believe, that all the most complex and wonderful instincts have originated. As modifications of corporeal structure arise from and are increased by use or habit and are diminished or lost by disuse, so I do not doubt it has been with instincts. But I believe that the effects of habit are in many cases of subordinate importance to the effects of the natural selection of what may be called spontaneous variations of instincts. That is, of variations produced by the same unknown causes which produce slight deviations of bodily structure. No complex instinct can possibly be produced through natural selection, except by the slow and gradual accumulation of numerous slight yet profitable variations. Hence, as in the case of corporeal structures, we ought to find in nature not the actual transitional gradations that each complex instinct has been acquired, for these could be found only in the lineal ancestors of each species. But we ought to find in the collateral lines of descent some evidence of such gradations, or we ought at least to be able to show that gradations of some kind are possible, and this we certainly can do. I have been surprised to find making allowance for the instincts of animals having been but little observed, except in Europe and North America. And for no instinct being known among extinct species, how very generally gradations leading to the most complex instincts can be discovered. Changes of instinct may sometimes be facilitated by the same species having different instincts at different periods of life, by different seasons of the year, or when placed under different circumstances, etc., in which case either the one or the other instinct might be preserved by natural selection. And such instances of diversity of instinct in the same species can be shown to occur in nature. Again, as in the case of corporeal structure, and conformably to my theory, the instinct of each species is good for itself, but has never, as far as we can judge, been produced for the exclusive good of others. One of the strongest instances of an animal apparently performing in action for the sole good of another, with which I am acquainted, is that of affidies voluntarily yielding, as was first observed by Huber, their sweet excretion to ants. They do so voluntarily, the following facts show. I removed all the ants from a group of about a dozen affidies on a dog plant, and prevented their attendance during several hours. After this interval, I felt sure that the affidies would want to excrete. I watched them for some time through a lens, but not one excreted. I then tickled and stroked them with their hair in the same manner as well as I could, as the ants do with their antennae, but not one excreted. Afterwards, I allowed an ant to visit them, and it immediately seemed, by its eager way of running about, to be well aware what a rich flock it had discovered. It then began to play with its antennae on the abdomen first of one aphis, and then of another. And each, as soon as it felt the antennae, immediately lifted up its abdomen and excreted a limpid drop of sweet juice, which was eagerly devoured by the ant. Even the quite young affidies behaved in this manner, showing that the action was instinctive, and not the result of experience. It is certain from the observations of Huber that the affidies show no dislike to the ants. If the latter be not present, they are at last compelled to eject their excretion. But as the excretion is extremely viscid, it is no doubt a convenience to the affidies to have it removed, therefore probably they do not excrete solely for the good of the ants. Although there is no evidence that any animal performs an action for the exclusive good of another species, yet each tries to take advantage of the instincts of others, as each takes advantage of the weaker bodily structure of another species. So again, certain instincts cannot be considered as absolutely perfect. But as details on this and other such points are not indispensable, they may be here passed over. As some degree of variation in instincts under a state of nature, and the inheritance of such variations are indispensable for the action of natural selection, as many instances as possible ought to be given, but want of space prevents me. I can only assert that instincts certainly do vary. For instance, the migratory instinct, both in extent and direction, and in its total loss. So it is with the nests of birds, which vary partly in dependence to the situations chosen, and on the nature and temperature of the country inhabited, but often from causes wholly unknown to us. Audubon has given several remarkable cases of differences in the nests of the same species in the northern and southern United States. Why it has been asked if instinct be variable has it not granted to the bee the ability to use some other material when wax was deficient? But what other natural material could bees use? They will work, as I have seen, with wax hardened with vermilion or softened with lard. Andrew Knight observed that his bees, instead of laboriously collecting propolis, used a cement of wax and turpentine with which he had covered decorticated trees. It has lately been shown that bees, instead of searching for pollen, will gladly use a very different substance, namely oatmeal. Fear of any particular enemy is certainly an instinctive quality, and may be seen in nestling birds, though it is strengthened by experience and by the sight of fear of the same enemy in other animals. The fear of man is slowly acquired, as I have elsewhere shown, by the various animals which inhabit desert islands, and we see an instance of this, even in England, in the greater wildness of all our large birds in comparison with our small birds, which have been most persecuted by man. We may safely attribute the greater wildness of our large birds to this cause. For in uninhabited islands, large birds are not more fearful than small, and the magpie, so wary in England, is tame in Norway, as is the hooded crow in Egypt, that the mental qualities of animals of the same kind, born in a state of nature, which could be shown by many facts. Several cases could also be induced of occasional and strange habits in wild animals, which, if advantageous to the species, might have given rise through natural selection to new instincts. But I am well aware that these general statements without the facts in detail can produce but a feeble effort on the reader's mind. I can only repeat my assurance that I do not speak without good evidence. Inherited changes of habit or instinct in domesticated animals, the possibility, or even probability, of inherited variations of instinct in a state of nature will be strengthened by briefly considering a few cases under domestication. We shall thus be enabled to see the part which habit and the selection of so-called variations have played in modifying the mental qualities of our domestic animals. It is notorious how much domestic animals vary in their mental qualities. With cats, for instance, one naturally takes to catching rats, and another mice, and these tendencies are known to be inherited. One cat, according to Mr. St. John, always brought home game birds, another hares or rabbits, and another hunted on marshy ground and almost nightly caught woodcocks or snipes. A number of curious and authentic instances could be given of various shades of disposition and taste, and likewise of the oddest tricks associated with certain frames of mind or periods of time. But let us look to the familiar case of the breeds of dogs. Be doubted that young pointers I have myself seen striking instances will sometimes point and even back other dogs the very first time that they are taken out. Retrieving is certainly in some degree inherited by retrievers and the tendency to run around instead of at a flock of sheep by shepherd dogs. I cannot see that these actions performed without experience by the young and in nearly the same manner by each individual, performed with ego delight by each breed and without the end being known. For the young pointer can no more know that he points to aid his master than the white butterfly knows why she lays her eggs on the leaf of the cabbage. I cannot see that these actions differ essentially from true instincts. If we were to behold one kind of wolf, when young without any training as soon as it scented its prey stand motionless like a statue and then slowly crawl forward with a peculiar gait and another kind of wolf rushing round instead of at a herd of deer and driving them to a distant point we should assuredly call these actions instinctive. Domestic instincts as they may be called are certainly far less fixed than natural instincts but they have been acted on by far less vigorous selection and have been transmitted for an incomparably shorter period under less fixed conditions of life. How strong these domestic instincts, habits and dispositions are inherited and how curiously they become mingled is well shown when different breeds of dogs are crossed. Thus it is known that a cross with a bulldog has affected for many generations the courage and obstinacy of greyhounds and a cross with a greyhound has given to the whole family of shepherd dogs a tendency to hunt hares. These domestic instincts when thus tested by crossing resemble natural instincts which in a like manner become curiously blended together and for a long period exhibit traces of the instincts of the parent. For example, Leroy describes a dog whose great-grandfather was a wolf and this dog showed a trace of its wild parentage only in one way by not coming in a straight line to his master when called. Domestic instincts are sometimes spoken of as actions which have become inherited solely from long-continued and compulsory habit but this is not true. Anyone would ever have sort of teaching or probably could have taught the tumbler pigeon to tumble an action which as I have witnessed is performed by young birds that have never seen a pigeon tumble. We may believe that some one pigeon showed a slight tendency to this strange habit and that the long-continued selection of the best individuals in successive generations is what they are now and near Glasgow there are house tumblers as I hear from Mr Brent which cannot fly 18 inches high without going head over heels. It may be doubted whether anyone would have thought of training a dog to point had not some one dog naturally shown a tendency in this line and this is known occasionally to happen as I once saw in a pure terrier as many have thought only the exaggerated paws of an animal preparing to spring on its prey when the first tendency to point was once displayed methodical selection and the inherited effects of compulsory training in each successive generation would soon complete the work and unconscious selection is still in progress as each man tries to procure without intending to improve the breed dogs which stand and hunt best. On the other hand habit alone in some cases has sufficed hardly any animal is more difficult to tame than the young of the wild rabbit scarcely any animal is tamer than the young of the tame rabbit but I can hardly suppose that domestic rabbits have often been selected for tameness alone so that we must attribute at least the greater part of the inherited change from wildness to extreme tameness to habit and long-continued close confinement. Natural instincts are lost under domestication a remarkable instance of this is seen in those breeds of fowls which very rarely or ever become broody that is never wish to sit on their eggs. Familiarity alone prevents our seeing how largely and how permanently our domestic animals have been modified. It is scarcely possible to doubt that the love of man has become instinctive in the dog. All wolves, foxes, jacals and species of the cat-genus when kept tame are most eager to attack poultry, sheep and pigs and this tendency has been found incurable in dogs which have been brought home as puppies from countries such as Chicago and Australia where the savages do not keep these domestic animals. How rarely on the other hand do our civilised dogs even when quite young require to be taught not to attack poultry, sheep and pigs. No doubt they occasionally make an attack and are then beaten and if not cured they are destroyed so that habit and some degree of selection have probably concurred in civilising by inheritance our dogs. On the other hand young chickens have lost wholly by habit that fear of the dog and cat which no doubt was originally instinctive in them. For I am informed by Captain Hutton that the young chickens of the parent stock the gallows spankiva when reared in India under a hen are at first excessively wild. So it is with young pheasants reared in England under a hen. It is not that chickens have lost all fear but fear only of dogs and cats for if the hen gives the danger chuckle they will run more especially young turkeys from under her and conceal themselves in the surrounding grass or thickets and this is evidently done for the instinctive purpose of allowing as we see in wild grandbirds their mother to fly away but this instinct retained by our chickens has become useless under domestication for the mother hen has almost lost by disuse the power of flight. Hence we may conclude that under domestication instincts have been acquired at natural instincts have been lost partly by habit and partly by man selecting and accumulating during successive generations peculiar mental habits and actions which had first appeared from what we must in our ignorance call an accident. In some cases compulsory habit alone has sufficed to produce inherited mental changes. In other cases compulsory habit has done nothing and all has been the result of selection pursued both methodically and unconsciously but in most cases habit and selection have probably concurred. Special Instincts We shall perhaps best understand how instincts in a state of nature have become modified by selection by considering a few cases. I will select only three namely the instinct which leads the cuckoo to lay her eggs in other bird's nests the slave making instinct of certain ants and the cell making power These two latter instincts have generally and justly been ranked by naturalists as the most wonderful of all known instincts. Instincts of the cuckoo It is supposed by some naturalists that the more immediate cause of the instinct of the cuckoo is that she lays her eggs not daily but at intervals of two or three days so that if she were to make her own nest and sit on her own eggs those first laid would have to be left for some time unincubated or there would be eggs and young birds of different ages in the same nest. If this were the case the process of laying and hatching might be inconveniently long more especially as she migrates at a very early period and the first hatched young would probably have to be fed by the male alone but the American cuckoo is a predicament for she makes her own nest and has eggs and young successively hatched all at the same time It has been both asserted and denied that the American cuckoo occasionally lays her eggs in other birds' nests but I have lately heard from Dr. Merrill of Iowa that he once found in Illinois a young cuckoo together with a young J garrulous Christatus and as both were nearly full feathered there could be no mistake in their identification I could also give several instances of various birds which have been known occasionally to lay their eggs in other birds' nests Now let us suppose that the ancient progenitor of our European cuckoo had the habits of the American cuckoo and that she occasionally laid an egg in another bird's nest If the old bird profited by this occasional habit through being enabled to emigrate earlier or through any other cause or if the young were made more vigorous by advantage being taken of the mistaken instinct of another species than when reared by their own mother encumbered as she could hardly fail to be by having eggs and young of different ages at the same time then the old birds or the fostered young would gain an advantage and the analogy would lead us to believe that the young thus reared would be apt to follow by inheritance the occasional and aberrant habit of their mother and in their turn would be apt to lay their eggs in other birds' nests and thus be more successful in rearing their young By a continued process of this nature I believe that the strange instinct of the cuckoo has been generated It has also recently been ascertained on sufficient evidence by Adolf Müller that the cuckoo occasionally lays her eggs on the bare ground sits on them and feeds her young This rare event is probably a case of reversion to the long lost Aboriginal instinct of nidification It has been objected that I have not noticed other related instincts and adaptations of the culture in the cuckoo which has spoken of as necessarily coordinated but in all cases speculation of an instinct known to us only in a single species is useless for we have hitherto had no facts to guide us Until recently the instincts of the European and of the non-parasitic American cuckoo alone were known Now, owing to Mr. Ramsey's observations we have learned something about three Australian species which lay their eggs in other bird's nests The chief points to be referred to are three First, that the common cuckoo with rare exceptions lays only one egg in a nest so that the large and voracious young bird receives ample food Secondly, that the eggs are remarkably small not exceeding those of a skylark a bird but one fourth as large as the cuckoo that the small size of the egg is a real case of adaptation we may infer from the fact of the non-parasitic American cuckoo lying full-sized eggs Thirdly, that the young cuckoo soon after birth has the instinct, the strength and a properly shaped back for ejecting its foster brothers which then perish from cold and hunger This has been boldly called a beneficent arrangement in order that the young cuckoo may get sufficient food and that its foster brothers may perish before they had acquired much feeling Turning now to the Australian species Though these birds generally lay only one egg in a nest it is not rare to find two and even three eggs in the same nest In the bronze cuckoo the eggs vary greatly in size from eight to ten lines in length Now if it had been an advantage to this species to have laid eggs even smaller than those now laid so as to have deceived certain foster parents or as is more probable to have been hatched within a shorter period for it is asserted that there is a relation between the size of eggs and the period of incubation Then there is no difficulty in believing that a race or species might have been formed which would have laid smaller and smaller eggs for these would have been more safely hatched and reared Mr. Ramsey remarks that two of the Australian cuckoos when they lay their eggs in an open nest manifest a decided preference for nests containing eggs The European species apparently manifests some tendency towards a similar instinct but not rarely departs from it as is shown by her laying her dull and pale coloured eggs in the nest of the hedge warbler with bright greenish blue eggs Had our cuckoo invariably displayed the above instinct it would assuredly have been added to those which it has assumed must all have been acquired together The eggs of the Australian bronze cuckoo vary according to Mr. Ramsey to an extraordinary degree in colour so that in this respect as well as in size natural selection might have secured and fixed any advantages variation In the case of the European cuckoo the offspring of the foster parents are commonly ejected from the nest within three days after the cuckoo is hatched and as the latter at this age is in a most helpless condition Mr. Gould was formally inclined to believe that the act of ejection was performed by the foster parents themselves but he has now received a trustworthy account of a young cuckoo which was actually seen while still blind and not able even to hold up its own head in the act of ejecting its foster brothers One of these was replaced in the nest by the observer and was again thrown out With respect to the means by which this strange and odious instinct was acquired if it were of great importance for the young cuckoo as is probably the case to receive as much food as possible soon after birth I can see no special difficulty in its having gradually acquired during successive generations the blind desire, the strength and the structure necessary for the work of ejection for those cuckoos which had such habits and structure best developed would be the most securely reared The first step towards the acquisition of the proper instinct might have been more unintentional restlessness on the part of the young bird when somewhat advanced in age and strength the habit having been afterwards moved and transmitted to an earlier age I can see no more difficulty in this than in the unhatched young of other birds acquiring the instinct to break through their own shells or than in young snakes acquiring in the upper jaws as Owen has remarked a transitory sharp tooth for cuttings for the tough egg shell for if each part is liable to individual variations of their ages and the variations tend to be inherited at a corresponding or earlier age propositions which cannot be disputed then the instincts and structure of the young could be slowly modified as surely as those of the adult and both cases must stand or fall together with the whole theory of natural selection some species of the monothrus a widely distinct genus of American birds allied to our starlings have parasitic habits like those of the cuckoo and the species present an interesting gradation in the perfection of their instincts the sexes of monothrus badius are stated by an excellent observer Mr. Hudson sometimes to live promiscuously together in flocks and sometimes to pair they either build a nest of their own or seize on one belonging to some other bird occasionally throwing out the nestings of the stranger they either lay their eggs in the nest thus appropriated or oddly enough build one for themselves on the top of it they usually sit on their own eggs and rear their own young but Mr. Hudson says it is probable that they are occasionally parasitic for he has seen the young of this species following old birds of a distinct kind and clamoring to be fed by them the parasitic habits of another species of monothrus the m-bonariensis are much more highly developed than those of the last but are still far from perfect this bird as far as it is known invariably lays its eggs in the nests of strangers but it is remarkable altogether sometimes commence to build an irregular untidy nest of their own placed in singular ill-adapted situations as on the leaves of a large thistle they never, however as far as Mr. Hudson has ascertained complete a nest for themselves they often lay so many eggs from 15 to 20 in the same foster nest that few or none can possibly be hatched they have moreover the extraordinary habit of pecking holes in the eggs whether of their own species or of their foster parents which they find in the appropriated nests they drop also many eggs on the bare ground which are thus wasted a third species the m-pecoris of North America has acquired instincts for it never lays more than one egg in a foster nest so that the young bird is securely reared Mr. Hudson is a strong disbeliever in evolution but he appears to have been so much struck by the imperfect instincts of the Mollithras' Bonariensis that he quotes my words and asks must we consider these habits not as especially endowed or created instincts but as small consequences of one general law namely transition various birds as has already been remarked occasionally lay their eggs in the nests of other birds this habit is not very uncommon with the Galanesi and throws some light on the singular instinct of the ostrich in this family several hen birds unite and lay first a few eggs in one nest then in another and these are hatched by the males this instinct may probably be accounted for by the fact of the hens laying a large number of eggs but as with the cuckoo at intervals of two or three days the instinct however of the American ostrich as in the case of the Mollithras' Bonariensis has not as yet been perfected for a surprising number of eggs strewed over the plains so that in one day's hunting are picked up near less than 20 lost and wasted eggs many bees are parasitic and regularly lay their eggs in the nests of other kinds of bees this case is more remarkable than that of the cuckoo for these bees have not only had their instincts but their structure modified in accordance with their parasitic habits for they do not possess the pollen-collecting apparatus which would have been indispensable if they had stored up food for their own young some species of sphagidi wasp-like insects are likewise parasitic and M. Faber has lately shown good reason for believing that although the tachitis nigra generally makes its own burrow and stores it with paralyzed prey for its own larvae yet that when this insect finds a burrow already made and stored by another's fex it takes advantage of the prize and becomes for the occasion parasitic in this case as with that of the molothras or cuckoo I can see no difficulty in natural selection making an occasional habit permanent if of advantage to the species and if the instinct whose nest and stored food are feloniously appropriated be not thus exterminated End of Chapter 8 Part 1