PART IV 

 ANIMAL LIFE 



20. FROM EGG TO ADULT 



Eggs of Animals. With the exception of the Protozoa, 

 all species produce specialized cells capable under certain 

 conditions of developing into new animals similar to the 

 parents. Such cells are known as ova or eggs. These are 

 so small in some of the invertebrates as to be invisible to 

 the naked eye, while in some of the fish the}' are as large 

 as a pinhead, and in reptiles and birds many times larger- 

 The egg of the alligator is more than two inches in diameter, 



FIG. 328. Eggs of vert 

 woodpecker 



tebrates, a, pond turtle ; b, black snake ; c, garter snake ; rf, 

 ; e, lizard. Photograph two thirds natural size. 



and that of the ostrich is more than six inches. The real 

 difference between the small egg of the fish and the large 

 egg of the bird is in the amount of the yolk and albumen 



