74 ORGANIC EVOLUTION — THE FACTORS' 



which arise from the proliferation of the germ cells, then 

 of course acquired variations cannot be transmitted, and 

 evolution can proceed only on lines of inborn varia- 

 tions. If it is not true, if the germ cells are in part 

 the products of the other co-existing cells, and receive 

 from them "gemmules," and acquired variations are 

 therefore transmissible, then besides the difficulties in 

 the way of belief caused, as already indicated, by the 

 incredible number of the assumed "gemmules," and 

 the difficulties in the way of belief due to the impossi- 

 bility of conceiving their arrangement in the germ cells, 

 we are faced by the further difficulty of explaining 

 when and by what method of evolution such a process 

 arose. Nothing like it can possibly occur among the 

 descendants of a pair of conjugated unicellular organ- 

 isms; if it exists at all it must have arisen de novo 

 among multicellular organisms of a high order, for 

 among lower multicellular organisms there exists no 

 vehicle for the conveyance of "gemmules" to distant cells. 

 The closer, therefore, the theory that acquired varia- 

 tions are transmissible is examined, the more incred- 

 ible on a priori grounds does it appear. The upholders 

 of it, however, allege that natural selection — i. e. the ac- 

 cumulation of inborn variations by natural selection — is 

 quite inadequate to account for evolution in its totality. 

 However this may be, and it is certainly disputable, the 

 fact remains, that the more our knowledge of nature 

 expands the better able are we to explain the whole 

 process of evolution by the accumulation of inborn vari- 

 ations alone ; moreover, those who maintain that many 

 cases of evolution are explainable only on the assump- 

 tion that acquired variations are transmissible, are 

 compelled to admit that in many cases of evolution, 

 more complex and far-reaching than any they instance 

 to the contrary, the accumulation of acquired variations 

 can have played no part. For instance, compare the 



