BEGINNINGS OF THE NEXT GENERATION 107 



motion. Each is a single cell — a sperm. Each seems to 

 have both head and tail, like a stretched-out tadpole. All are 

 so small that it takes six thousand sperm heads placed side 

 by side to measure one inch. When they have the chance 

 for it, each is ready to join an egg, and together they start 

 life for a new fish. This is called fertilization. 



Now in a general way this history of .fish beginnings is 

 really the history of the beginning of every vertebrate, man 

 included. There is never any confusion in results. The indi- 

 vidual started by fish parents becomes a fish, while birds and 

 beasts and each separate kind of human being have children 

 according to their kind. This law of life does not vary. It 

 is immutable. 



It is of course true that the first. two cells do not always 

 come upon one another by the same road. With fish they 

 are deposited side by side in water. This is ill that is neces- 

 sary. They reach each other, and young fish begin to develop. 



With birds and other animals there is another arrange- 

 ment. Since the environment of creatures that do not live 

 in water is always dry, and since germ cells must not be al- 

 lowed to get dry even if they do belong to dry land animals, 

 nature provides for this. The germ cells of these animals 

 pass directly from one individual to another. 



A further point is that germ cells which are to carry on the 

 life of the race — whether of fish or of any other creature — 

 must stay in damp surroundings from the time they meet 

 until the individual is formed. Nature brings this about in 

 three different ways : 



1. With fish and frogs the eggs stay in the water and 

 develop there. 



2. With birds and reptiles a stout shell is supplied. This 

 shell grows about the germ cell within the body of the mother, 



