THE DOCTRINE OP IMMORTALITY 



49 



since in them also there occur slightly differentiated cells 

 which are appUed for the formation of sexual cells. The 

 other cells, which constitute by far the majority, we name 

 the somatic cells, and therefore say that every animal body 

 consists of many somatic and a few sexual cells. It we pass 

 from the lower to the higher animals, we find that the separa- 



Germ-Cellc 



Jplk: 



Fig. 23 . — Section through the posterior part of an embryo of the dog-fish, Squalus 

 acanthias. Germ cells designates the group of sexual cells which have united in one 

 group, which still lies far from the position of the future sexual gland. Ect, ectoderm; 

 Md, spinal cord; Nch, axis of the body (notochord); Mes, mesoderm; Ent, entoderm; 

 Yolk, yolk-mass. 



tion of the two classes of cells, the names of which we have 

 just heard, becomes sharper. We have succeeded recently in 

 observing the precocious separation, or isolation, of the sex 

 cells in vertebrates. Their number is very small in propor- 

 tion to the number of somatic cells. In the young embryo 



