84 Heredity. 



gemmule may unite or conjugate in the ovum with 

 particles which are not perfectly equivalent to it, but 

 only very closely related to it. Thus a variation may 

 affect a considerable number of related cells at the same 

 time, or a variation in any part may cause in succeeding 

 generations the variation of homologous parts, thus pro- 

 ducing what Darwin has called correlated variation. We 

 can also understand how it is that when any part of a 

 complicated organ varies, variations in other parts of it 

 are also soon presented for the action of natural selec- 

 tion, so that an harmonious readjustment is soon estab- 

 lished. 



According to this view we must believe that all the 

 characteristics which are established as true race- 

 characteristics, as hereditary peculiarities of the species, 

 are transmitted by the ovum, which has in itself the 

 power to develop, when excited by a proper stimulus 

 which may or may not be due to impregnation, into a 

 new individual of the parent form. 



New variations, on the other hand, are produced 

 through the agency of gemmnlcs thrown off from cells 

 like those in which the variation appears. 



Gemmules may penetrate to all parts of the body, and 

 they may thus give rise to bud-variation and to analogous 

 changes; or they may penetrate to an ovarian ovum 

 and give rise to variation without fertilization: but as 

 these phenomena depend upon chance, they are com- 

 paratively rare, while the aggregation of the gemmules 

 in the male cell and their transmission by impregnation 

 are normal processes. 



According to this view, the male element is the origi- 

 nating and the female the perpetuating factor; the 

 ovum is conservative; the male cell progressive. Hered- 

 ity or adherence to type is brought about by the ovum; 



