 Well, in descriptive embryology, the next topic that is about the amphibian embryology, i.e. if a frog, a toad, or a slum mender study its embryology, these are the different stages of development. Or amphibian embryology, or just like in econodrome embryology, one can very easily study the development process in the lab. And especially if the conditions are duplicated in the lab, we can very easily observe the stages of development in an earthenware pot, in which there is water, and if we put fertilized eggs in it, then these cells will start dividing. And in this diagram, we are seeing that the first stage, there is the fertilized egg and then there is a meridional cleavage, on the upper half, this is the animal pole, and the lower half is the veritable pole, this is the animal pole, and this is the veritable pole. And then there is a third cleavage, which appears at right angles to the first, and then there is a third cleavage, which is equatorial, and as soon as this equatorial cleavage appears, then the embryo will be called the eight-celled stage. And in this, we are seeing that the upper cells, which are the micromials and lower cells, they are the macromials. In this, we are observing that the yoke is actually towards the vegetal pole. And this yoke prevents the process of the cleavage or slows the process of the cleavage, and because of this, the cells that are called the micromials, they start dividing more quickly as compared to the macromials or the vegetal, that is the cells. Now at this stage, at this stage, where micromials and macromials can differentiate from the size of the leha, then there appears a dent, this dent appears, and this dent, this is the start of the Arkinthiruan justice, and then there is the start of the gut, and these micromials they start spreading over the macromials, and slowly, slowly, this first stage becomes a crescent shape, and after that, as the micromials start spreading over the macromials, so ultimately this stage, it is a stage like this that appears, and this is the part which is said to be the dorsal lip of the blastopore, this is the ventral lip, and these are lateral lips of blastopores. This port you have, this is a very important port, which is the start of the, that is the development process, or the second cleavage, the cleavage process, the animal region becomes packed with numerous small cells, with the vegetal region contains only relatively small number of large yolk-laden macromials, which we have mentioned, so when these cells are formed, then that is called as morula, morula is from mulberry, like a small rounded mulberry, like that is the same, on the same base, what is the word morula, what is it? Now at the 128 cell stage, the blasto-seal becomes apparent, that is, here a cavity appears inside towards the animal pole, so this is what we call the blasto-seal, that becomes apparent and embryo is considered a blasto-lock, okay. Now the blasto-seal that probably serves two major functions, that is infrog embryos, or these major functions, it permits cell migration during gestulation, it permits the movement, the migration of the cells, also the second is, it prevents the cells beneath it from inter, that is, acting permanently, prematurely, with the cells above it, so they remain, they keep it separate, so these are the two functions of this blasto-seal, and this blasto-seal is water-filled, it is not just a space, it is water-filled cavity, after that the process comes to gestulation, what is gestulation, this is the movement of cells, this is the movement of cells, literally, cells move from one place to the other, and ultimately a three-layered embryo is formed, and when this three-layered embryo is formed, then we give it the name of gestula, and in the last diagrams, we saw from the outside, super-visually, how it appears to be, because when it is developing, in a vat or in an earthenware pot, we can magnify it, so it looks very good to look at, so after that, if we keep it under observation, then there are beautiful changes, they continue to appear, but we have to see what is going on inside the embryo, because we have seen that it has become a blastopore, now we have to see it in this, and we fix these embryos on the main stages, and then cut the sections of the embryo, and then we know what is going inside the embryo, and this is what is going inside the embryo, and this is a ball that we have cut vertically, and this is the dorsal lip of the blastopore, as we have seen in the diagram from the beginning, and from here, the cells start migrating inward, and these cells differentiate, which we call the bottle cells, so bottle cells, they are the cells, as these are the bottle cells, this is the developed stage, they are the leaders, and this is the blasto seal that appeared inside the embryo, and this is the dorsal lip of the blastopore, and these cells, which are in fact outside, then they will start migrating inwards, and in this way, we call it a tube, then we call it Archantyron, and as it increases, and the blasto seal will get obliterated, and this Archantyron will develop, and in this way, these cells, this embryo, it becomes differentiated into three layers, and any actodermal cell will not move inside, the cells that enter from the lower lip of the blastopore, they will be the endodermal cells, and the dorsal lip of the blastopore, they will be the mesodermal cells, and in this way, the gastrulation that begins at the future dorsal side, okay, now below the equator, where the prospective endodermal cells, as the bottle cells, and form a slit, which we call the blastopore, the bottle cells line the early Archantyron, now number two, after the bottle cells, the next cells that enter the embryo, they form the pre-cordal, that is plate, and the mesodermal of the dorsal cord, because the notocard is mesodermal in origin, so it develops the notocard from the mesodermal. Now simultaneously, the animal cells undergo epibolli, we did not take the name of epibolli, but when the micromere starts spreading over the micromere, so this movement, and ultimately the blastopore, we call it the yolk plug, which we saw in the very early stage, in the first slide, so this is what we call the epibolli, epibolli it is a movement, specialized movement of cells, particularly in amphibians, so this is why it becomes a blastopore, and as we said, there is dorsal lip of the blastopore, there is a ventral lip and the lateral lip of the blastopore, and from these blastopores, the cells enter the embryo, and some cells, they are moving inside through the ventral lip of the blastopore, some lateral lip of the blastopore, and then they spread, and in this way, these three layered embryos are formed, the last endodouble cells on the surface appear on, that is as the as the yolk plug, the yolk plug is eventually covered by acrodome, or ultimately, it is it is overlapped, it is covered by the acrodome, and the thing to remember is that acrodome cells, any acrodome cell does not enter inside the embryo, because this is the acrodome which is to develop then into the nervous system, when we call it an organogenesis process, then the early embryology is up to the gastrolysis, up to the gastrolysis we have studied, how the gastrolysis occurs, and how the three layered embryos are formed, and these acrodome, medodome, and endodome, three clear layers are formed, and then when these three layered embryos are formed, then every layer that starts changing into different structures, which we will discuss later, so this is all about the amphibian embryology.