THEORIES OF HEREDITY 



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is always the same for any given species, and has been 

 called by Weismann the " germ-track." Fig. 36 will make 

 this clear. We have, then, if not a continuity of germ-cells, 

 as in the first-mentioned cases, a " continuity of the germ- 



F IGt 36. DIAGRAM OF GERM-TRACK OF RHABDITIS NIGROVENOSA. 

 (From Weismann, " The Germ-Plasm.") 



The primitive mother-cell (Eiz) divides into the primitive ectoderm 

 cell (urEkt) and the primitive entoderm cell (urEnt), the former 

 forming the cells of the ectoderm (Ekt, white), and the latter 

 those of the entoderm (Ent, black). The primitive entoderm 

 cell (urEnt) further forms the primitive mesoderm cells 

 (3', 4', 5", urMes), which in their turn give rise firstly to the 

 mesoderm (Mes, rings with dots), and secondly to the primitive 

 germ-cells (urKzg), from which arise finally the germ-cells 

 (Kz, black rings). 



plasm." Contrary to the commonly-held opinion that the 

 body creates the germ-cells, the body must, according to 

 Weismann, be considered a product of the germ. It may 

 conveniently be pictured (see the accompanying diagram 



