74 MAN, — THE ANIMAL 



form new generations there would be no such thing 

 as we now recognize as living protoplasm. This 

 feature of life is to be considered in just the same 

 sense that one regards the power of living things 

 to secure nourishment, to respond to stimuli, 

 etc. It is a grave mistake to try to separate re- 

 production from the other characteristics of life 

 and discuss it as something special. It can never 

 have its correct relations except when the several 

 aspects of life are considered together. 



Let us examine these germ cells in some detail 

 in order that there may be a foundation for under- 

 standing the marvelous results that come from 

 them. The egg cell or ovum is the more satisfac- 

 tory for beginning this study because of its size. 

 In Fig. 1 8 is shown a photograph of a small, 

 rounded cell with a conspicuous nucleus and a rela- 

 tively small amount of cytoplasm. This is a 

 young stage in the growth of the egg cell of one 

 of the common worms. For a long time, possibly 

 several years, this cell was cylindrical in shape and 

 smaller than it is now. There were many other 

 cells just like if in the ovary of the worm. Neither 

 internal nor external agencies are held responsible 

 for selecting this cell from the many others to be- 

 come changed into a germ cell. When such cells 

 are studied, the larger rounded ones are the ones 

 upon which attention is fixed. In Fig. 19 a later 

 stage in the growth of an egg in this same animal 



