92 MAN, — THE ANIMAL 



cessful in entering the egg. It is evident that the 

 result will be determined when this union takes 

 place. If one wishes to be facetious, he can con- 

 gratulate himself as to his existence and that he is 

 what he is and not a different individual as he cer- 

 tainly might have been if a different sperm had 

 united with the ovum because it is very generally 

 accepted by scientists that nature never yet made 

 two eggs or two sperms exactly alike. 



As long as animals lived in the water, it was a 

 simple matter to bring the sperms and eggs to- 

 gether. The fish deposits her eggs in the water 

 and one or more males discharge vast quantities 

 of sperms in the same vicinity. In a similar man- 

 ner, the eggs of frogs are brought in contact with 

 the sperms, water being the only medium necessary 

 to bring the eggs and sperms together. But when 

 animals came to live on land two new problems 

 arose. One was that of bringing sperms and eggs 

 together, because the cells are heavier than air and 

 are unable to move about in the ground; the other 

 was that of protecting and nourishing the embryo. 

 The first stage in solving the latter problem con- 

 sisted in furnishing membranes and shells, with 

 adequate food for the embryo till it hatched. The 

 eggs of snakes, turtles, and birds illustrate this 

 stage. The highest form of protection to the em- 

 bryo is in man where all of the embryonic changes 

 take place in the uterus of the mother. 



