126 



Heredity and Environment 



Gametti O \V 



*\t 



Zygote 



ABCD 



Fig. 41. Diagram Show- 

 ing the "Cell Lineage" of 

 the Body Cells and Germ 

 Cells in a Worm or Mol- 

 lusk. The lineage of the 

 germ cells ("germ track") 

 is shown in black, of ecto- 

 derm in white, and of endo- 

 derm and mesoderm in 

 shaded circles. The whole 

 course of spermatogenesis 

 and oogenesis is shown in 

 the lower right of the figure 

 beginning with the primitive 

 sex cells {Prim. Sex Cells) 

 and ending with the gam- 

 etes, the genesis of the sper- 

 matozoa being shown on the 

 left and that of the ova on 

 the right. 



Off** 



l*Mal / \. 



Cyies 11m m 



Gametes 



ditions. The body develops and dies in each generation ; the 

 germ-plasm is the continuous stream of living substance which 

 connects all generations. The body nourishes and protects the 

 germ ; it is the carrier of the germ-plasm, the mortal trustee of an 

 immortal substance. 



4. Genu plasm and Somatoplasm. — This contrast between the 

 germ and the body, between the undeveloped and the developed 



