METAZOA 97 



119. Potential Immortality of Germ Cells. — Germ cells possess a 

 potential immortality, since any germ cell has the capacity under proper 

 conditions to take part in the production of another individual, and 

 this may continue for an indefinite number of generations. Neverthe- 

 less, they perish in enormous numbers, since many eggs are never fer- 

 tilized and a greater number of sperm cells never find an egg cell with 

 which to unite. In contrast to germ cells, somatic cells present no possi- 

 bility of life beyond the lifetime of the individual of which they are a 

 part. The distinction between germ cells and somatic cells, or, more 

 exactly, between germ plasm and somatoplasm, was emphasized by 

 Weismann (Sec. 118). He also stressed the independence of the germ 

 cells and Hkened the body, or soma, to a vehicle for the nourishment 

 and transmission of germ cells. The hereditary units, which determine 

 the possibilities open to the animal, are passed from generation to 

 generation in the germ cells, whereas in the various types of somatic 

 cell, under the environmental conditions which surround each, are 

 reahzed and manifested such of these possibilities as, taken together 

 equip the individual with its characteristic features. 



