THE GERM-PLASM THEORY 291 



tureless body from which both the body and the ova 

 of the individual evolve ; and considered these ova 

 to consist of contributions partly from the egg and 

 partly from the body which developed from the egg. 

 Later Jager (1877) stated the idea of germinal con- 

 tinuity more definitely. He maintained that part 

 of the germ-plasm (Keim Protoplasma) of the 

 animal forms the individual, and the rest is re- 

 served until sexual maturity, when it forms the repro- 

 ductive material. The reservation of this phylo- 

 genetic substance he termed the "continuity of 

 the germ-plasm" (*'Continuitat des Keimproto- 

 plasmas"). To Weismann (1885) is usually given 

 the credit for originating the germ-plasm theory, 

 but while we are undoubtedly indebted to him for 

 the great influence the hypothesis of germinal con- 

 tinuity has had upon the trend of biological investi- 

 gations within the past tliirty years, we must con- 

 sider Jager as the first to clearly enunciate the idea. 

 Jager (1878) also expressed a belief in the mor- 

 phological continuity of the germ cells of succeed- 

 ing generations, but this idea was first definitely 

 stated by Nussbaum (1880), whose investigations 

 of the germ cells in the trout and frog led him to 

 conclude that the cleavage cells form two groups 

 independent of each other. One group contains 

 the cells which multiply and differentiate and thus 

 build up the body of the individual, but do not pro- 

 duce germ cells ; the other group takes no part in 

 the formation of the body and undergoes no differen- 

 tiations, but multiplies by simple division. The germ 



