VARIATION 



415 



diiference. If we suppose this process to go on in the various 

 parts of the body, the transformation of a species would thus be 

 accounted for.* 



The production of races by artificial selection appears, in fact, 

 to be in part due to such an accumulation of parental ' charac- 

 ters ' ; but I shall show later on that it is not accompanied by 

 an actual variation of the determinants, which alone could 

 gradually lead to a transformation of the species. We know that 

 the paternal and maternal idants do not fuse in the process of 

 amphimixis, and the immense number of cases of perfect trans- 

 mission proves that the determinants of both sides undergo no 

 alteration by being brought together. The modification of the 

 determinants is a process which is not directly connected with 

 sexual intermingling, but follows its own course, and must be 

 due to special causes. 



This is made still clearer if we reflect that the lower organisms 

 — e.g., sponges and polypes — must possess a very small number 

 of determinants compared to those in higher forms, such as 

 birds and mammals. The number of determinants in an id 

 of germ-plasjn has therefore increased considerably, and even 

 enormously, in the course of phyletic developnient. A single 

 peacock's feather may possibly be controlled by as many de- 

 terminants as an entire polype. Amphimixis alone, however, 

 could never produce a multiplication of the determinants. 



The cause of Jiereditary variation must lie deeper than this ; 

 it must be due to the direct effect of external influences on the 

 biophors and determinants, which I imagine to take place in the 

 following way. 



The entire substance of the earliest organisms must have 

 consisted of equivalent biophors, the nucleus and cell-body not 

 having yet become diiferentiated. In these lowest forms, whether 

 they exist or not at the present day, the perfect constancy of the 

 composition of the body may occasionally have been disturbed 

 by external influences of different kinds, and these modifications 

 must have been preserved, as they persisted in the two parts 

 resulting from reproduction by binary fission. 



When the morphoplasm and idioplasm subsequently became 

 differentiated, and the latter was enclosed in the nucleus as the 



* Compare my essay ' Die Bedeutung der sexuellen Fortpflanzung," Jena, 

 1866, p. 40. English edition, Oxford, 1889, p. 279. 



