882 PKOYTSTONAL HYPOTHESIS Chap. XXV1L 



sexual elements agree in power, in accordance with, the view 

 that both include the same geninmles. Hybrids and mongrels 

 are also generally intermediate in character between the two 

 parent-forms, yet occasionally they closely resemble one 

 parent in one part and the other parent in another part, or 

 even in their whole structure : nor is this difficult to under- 

 stand on the admission that the gemmules in the fertilised 

 germ are superabundant in number, and that those derived 

 from one parent may have some advantage in number, 

 affinity, or vigour over those derived from the other parent. 

 Crossed forms sometimes exhibit the colour or other characters 

 of either parent in stripes or blotches ; and this occurs in 

 the first generation, or through reversion in succeeding bud 

 and seminal generations, of which fact several instances were 

 given in the eleventh chapter. In these cases we must 

 follow Naudin, 57 and admit that the " essence" or " element" 

 of the two species, — terms which I should translate into the 

 gemmules, — have an affinity for their own land, and thus 

 separate themselves into distinct stripes or blotches; and 

 reasons were given, when discussing in the fifteenth chapter 

 the incompatibility of certain characters to unite, for believing 

 in such mutual affinity. ^Yhen two forms are crossed, one 

 is not rarely found to be prepotent in the transmission of 

 its characters over the other; and this we can explain by 

 again assuming that the one form has some advantage over 

 the other in the number, vigour, or affinity of its gemmules. 

 In some cases, however, certain characters are present in the 

 one form and latent in the other ; for instance, there is a 

 latent tendency in all pigeons to become blue, and, when a 

 blue pigeon is crossed with one of any other colour, the blue 

 tint is generally prepotent. The explanation of this form of 

 prepotency will be obvious when we come to the considera- 

 tion of Eeversion. 



AY hen two distinct species are crossed, it is notorious that 

 they do not yield the full or proper number of offspring ; 

 and we can only say on this head that, as the development 

 of each organism depends on such nicely -balanced affinities 



17 See his excellent discussion on this subject in ' Xouvelles Archives di 

 Museum,' torn. i. p. 151. 



