56 Hypothetical Bearers of Specific Characters 



of reproduction, this, according to Weismann, need not be 

 the case. On the contrary, from the one-sided differen- 

 tiation of these cells, he believes that there is a corre- 

 sponding reduction of their germ-plasm. Every somatic 

 cell receives, at the time of its origination, only those 

 hereditary elements which will be needed by itself and its 

 descendents. 



Against this assumption objections have been raised 

 from different sides, and some of them we shall describe 

 in detail in the Section on cellular pedigrees. Here, how- 

 ever, we must enter into the principal phase of the ques- 

 tion, namely, the relation of the ancillary hypotheses to 

 the main principle of the author. 



That principle is the assumption of units, of which 

 every one is capable of reproducing all, or at least nearly 

 all, hereditary characters of the species. There is sup- 

 posed to be, for each individual, only one hereditary sub- 

 stance, only one material bearer of the hereditary tenden- 

 cies. 24 To be sure, this is composed of ancestral plasms 

 which differ only slightly. A check must necessarily be 

 put to an excessive accumulation of various hereditary 

 tendencies by some kind of an arrangement. But, as we 

 have seen in our first section, the differentiation of the 

 organs demands the divisibility of the units of the germ- 

 plasm, and this in exactly the same high degree that the 

 differences of the individual organs and cells of an or- 

 ganism reach themselves. In the somatic cells the germ- 

 plasm must therefore gradually become divided into those 

 components, and hence, these are the bearers of the in- 

 dividual hereditary characters. 



Let us continue to build a few moments longer on this 

 conclusion, without reference to the chief assumption. In 



2 *Ueber die Zahl der Richtungskorper, p. 29. 



