 Amphibian embryology, cleavage, first the contents, holobolastic cleavage, radial cleavage, and plan up cell divisions. So first, students, we will talk about how the cleavage process starts in the amphibians. So normally the egg when it is fertilized by the sperm, this sperm also initiates the activation of the egg, due to which the egg starts the cell division and then the developmental process starts. Experimentally, it is seen that if the sperm is not available in most experiments, simply if we prick the egg with a needle, the developmental process starts, the cleavage process starts. It means that if the sperm or any other stimulus needle is activated by the egg, the cell division process starts. The initial cell division is actually called cleavage. The definition of cleavage is that it is a process of cell division. This is the process of cell division in which the zygote or fertilized egg which forms a number of cells, a ball of cells which becomes, or the next stage is called the morula stage. Now if we look at the pattern of the cleavage in amphibians, amphibians have moderate amount of yolk. Amphibians have moderate amount of yolk, they are actually the mizolacythal eggs because of which when the cleavage pattern comes, the cell division, the zygote will be completely divided into two cells. The zygote is divided into two cells, so this pattern of cleavage is called the holoblastic cleavage. It is called holoblastic cleavage. Usually, the cleavage or the cell division process starts with animal pores and comes towards the vegetal pole. So because of the amount of yolk, the cleavage towards the vegetal pole will be a little slow root but again the cell will be divided into two portion, the cell will be divided into two portion. Second important thing in cleavage, the number of cells that are formed in the cleavage, usually the cells are formed in the tires, in the tires, in the drawer, in the circle of the cell, in the circle of the other cell, the cleavage, it may be spiral, it may be radial cleavage, so the amphibians or the other coordinates, but deuterostromes which we say will come from the anodromes, so in deuterostromes, the pattern of cleavage is actually the radial cleavage, the amphibians which belong to deuterostromes, so in these also it will be radial cleavage. Radial cleavage, especially its identity is that if there is a lower tire of cell, then the tire of the cell will be exactly above it like this, so one cell will be above the other cell, one cell will be above the other cell, so like this, the lower tire and upper tire of the cell will be in exactly the same line, if they are arranged, then what we will call this type of cleavage, it is called radial cleavage. Radial cleavage is usually called indeterminate, indeterminate means that you cannot assume in the beginning that which cells are going to make which structure. Okay, now we see how the cleavage process starts, we have seen the pattern of the globulastic and then there will be radial cleavage, from where it will start, the first cleavage the first cell division, in that the cleavage process will start from the animal port and if it will move straight downward, and it will come down, that means the cleavage will start from the animal port and it will move towards the vegetal pole. First cleavage will be vertical, vertical means it will start from the top and from the animal pole, it will come towards the vegetal pole. Second cleavage will be at the right angle of the first cleavage, that means if it is from one side, the other will be vertical, but the first one will be at the right angle. This is like the sign of plus, one cleavage, if it is coming like this, then the second cleavage is coming like this, so the first cleavage is actually the vertical cleavage, they are starting from animal pole and moving towards the vegetal pole. Third cleavage is actually the horizontal cleavage, third cleavage will be horizontal and it passes from between animal and vegetal pole, so third cleavage will be horizontal and it will separate the cells of animal pole and the part of the vegetal pole. So the cells of animal pole will be faster in the later cell division because they have less yoga, the cells of the vegetal pole will proceed in the later cell division, that is why their size is usually larger because the amount of yoga is more. So the fourth cleavage, if we talk about it, then the fourth cleavage, it is again from the longitudinal direction or the vertical direction, we can call it, it will be top to bottom and divide the hard cell into two parts. So the first cleavage will be two cells, when the second cleavage will be, it will form four cells, third cleavage will be eight cells, the top part will be four, the lower part will be four. The fourth cleavage will divide the hard cell into two parts, so the top four cells will make eight cells and the bottom four cells will also make eight cells, so we have a total of sixteen cell stages after the fourth cleavage. The fifth cleavage is again horizontal and after that, after the 32 cell stage, the cell division will be rapid, the specific pattern will not remain of the cleavage. Usually, we can divide the third, fourth and fifth cleavage into a specific pattern. Here, we can see diagrammatically how this is the fertilized egg, animal pole, you can see the gray color, the vegetal pole, yellow color, both have gray characteristics. The second cleavage is starting from the animal pole to the vegetal pole. The second cleavage is coming at the right angle of the first cleavage. After physics, we have the third cleavage and after that, the pattern of the further cleavage will start. The two diagrams that are crossed at the end are actually the parts of the cleavage that I have crossed.