386 PROVISIONAL HYPOTHESIS Chap. XXVII. 



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the admission that the gemmules in the fertilised germ are 

 superabundant in number, and that those derived from one 

 parent 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 may occur in the first generation, or 



h reversion in succeeding bud and seminal generations, 

 as in the several instances given in the eleventh chapter. In 

 these cases we must follow Naudin, 42 and admit that the 



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"essence" or "element" of the two species, which terms I 

 should translate into the gemmules, have an affinity for their 

 own kind, and thus separate themselves into distinct stripes or 

 blotches ; and reasons were given, when discussing in the fif- 

 teenth chapter the incompatibility of certain characters to unite, 

 for believing in such mutual affinity. When two forms are 

 crossed, one is not rarely found to be prepotent in the transmis- 

 sion of character over the other ; and this we can explain only 

 by again assuming that the one form has some advantage in the 

 number, vigour, or affinity of its gemmules, except in those 



cases, where 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 pre- 

 potent. When we consider latent characters, the explanation 

 of this form of prepotency will be obvious. 



When one species is crossed with another 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 between a 

 host of gemmules and developing cells or units, we need not 

 feel at all surprised that the commixture of gemmules derived 

 from two distinct species should lead to a partial or complete 

 failure of development. With respect to the sterility of hybrids 

 produced from the union of two distinct species, it was shown in 

 the nineteenth chapter that this depends exclusively on the 

 reproductive organs being specially affected ; but why these 

 organs should be thus affected we do not know, any more than 



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42 See his excellent discussion on this subject in < Nou veil es Archives du 

 Museum,' torn. i. p. 151. 





