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- 



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Fig. 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 (urEni), the former 

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

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

 cell [iirEnt) further forms the primitive mesoderm cells 

 (3'^ A'y S" ) 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 



