126 



Heredity and Environment 



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Zygot* 



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. 



Omutw 



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. Germplasm and Somatoplasm. This contrast between the 

 germ and the body, between the undeveloped and the developed 



