THE HEREDITARY BASIS 13 



the germ cells, but the germ cells were held to receive their store 

 of pangens from antecedent germ cells. The denial of the flow of 

 pangens from the body to the germ cells did away with the means 

 by which Darwin accounted for the transmission of acquired or 

 somatogenic characters. De Vries did not hesitate to accept the 

 logical consequence of his hypothesis although he dwelt compara- 

 tively little on this feature of his doctrine. 



It is in the writings of Professor August Weismann that we 

 find the opposition to Lamarckism taking the form of vigorous 

 and sustained attacks. Weismann in his early essay On Heredity 

 set forth a very simple and plausible theory of transmission in his 

 doctrine of the continuity of the germ plasm. This conception 

 had been put forth previously by several writers (Owen, Galton, 

 His, Nussbaum, Jager, Rauber), but it did not attract much 

 attention until expounded in the lucid and attractive essays of 

 Weismann who made it the basis of a series of brilliant and elabo- 

 rate speculations on the mechanism of hereditary transmission. 

 Weismann taught that the germ plasm is a substance separate 

 from the soma plasm which forms the organs of the body, and 

 that it is in no way the product of the body, although it is carried 

 and nourished by the body. Germ plasm is handed on relatively 

 unchanged from one generation to the next, part of it being trans- 

 formed into soma plasm which differentiates in various ways 

 during embryonic development, but another part of it remaining 

 undifferentiated in the germ cells to form the starting point of the 

 next generation. Some germ plasm is, therefore, handed on in a 

 continuous stream through successive generations, the bodies 

 of the parents acting as "trustees of the germ plasm." It is the 

 continuity of the germ plasm that affords the basis for heredity. 

 Parent and offspring resemble each other not because the off- 

 spring are, in any sense, the product of the parent's body, but 

 because both parent and offspring arise from a common substance, 

 the germ plasm. Poulton has aptly said that Weismann's theory 

 makes the offspring the younger brothers and sisters of their 

 parents. We might compare successive generations to a series 

 of plants arising from an underground runner or root stalk. 



