82 MAN, THE ANIMAL 



potential new plant or animal. Both the parent 

 bodies, egg and sperm ^ were alive; and when they 

 unite their living protoplasm, a new individual is 

 produced that is alive. To destroy an embryo, 

 then, is to destroy life. 



In pointing out what happens after the union 

 of the egg and sperm, some illustrations in the de- 

 velopment of the large American salamander are 

 given. These photomicrographs show some of 

 the external changes which the embryo of this 

 animal passes through. In Fig. 26-A note that the 

 mass is being cut into halves. This will result in 

 forming an embryo whose body consists of two 

 cells. Such a figure only indicates some of the 

 superficial changes; more important ones are tak- 

 ing place within the nucleus. Some of the im- 

 portant internal changes are indicated in the ex- 

 cellent photomicrograph in Figs. 20-22. This is 

 a picture of the separation of the chromosomes 

 preparatory to the forming of the constriction in 

 the cytoplasm as shown in Fig. 2 6 A. There is 

 formed an elaborate mechanical structure whose 

 main purpose is to distribute the chromatin in 

 equal amounts to the new cells that are to form. 

 (Fig. 26G.) By this means each nucleus in the 

 embryo is furnished with the same number of 

 chromosomes. Every cell of the many thousands 

 of cells in the body of man has the same number 



