160 MENDEL'S LAWS 



only drones ; while, presumably, male characters are permanently 

 latent in such species as propagate only by parthenogenesis. 



273. Now the presumption is that the inheritance of the Men- 

 delian characters is of the same type as that of the sexual characters, 

 and therefore that, instead of segregation and gametic purity, what 

 really occurs is patency and latency}- If that be the case the 

 recessive character, which is temporarily latent in the * impure ' 

 dominant, is permanently latent in a line of * pure ' dominants, 

 whereas, on the other hand, the dominant is permanently latent in 

 the recessives permanently latent, that is, until the conditions 

 which bring about such latency are disturbed in much the same 

 way as when the conditions of latency of the female characters in 

 the ova of the bee are disturbed by fertilization, or those which 

 bring about the latency of the male characters in the summer ova 

 of aphides are disturbed by the advent of winter. If this be true, 

 the independent inheritance of characters on which Mendelians 

 insist is a myth. There is only independent development, inde- 

 pendent patency and latency. When, therefore, one variety is 

 crossed with another and the descendants show the varietal 

 characters in new combinations, all the alternative characters of 

 both varieties are present, but only a half of them are patent, and 

 this half includes characters from both species. 



274. Evidence more direct than that furnished by analogy is 

 not lacking. Contrary to what was formerly believed, the { ex- 

 tracted ' pure dominants and recessives of the second and succeeding 

 generations are rarely without traces of the alternative characters. 

 They are in truth real mongrels (not only as regards the whole 

 individual, but as regards each separate character) in which one or 

 more of the characters of one of the crossed varieties predominates 

 more or less, the degree of this predominance varying from an 

 absolute, or almost absolute completeness that approaches the 

 commonly complete dominance of the sexual characters, to a 

 blend intermediate between the crossed varieties. Thus in the 

 case of poultry, " very frequently, if not always, the character that 

 has once been crossed has been affected by its opposite with which 

 it was mated and whose place it has taken in the hybrid. It may 

 be extracted, therefrom, to use in a new combination, but it will be 

 found altered. This we have seen to be true for almost every 

 character sufficiently studied for the comb form, the nostril form, 



1 1 made this suggestion in the second edition of The Principles of Heredity 

 (Appendix B) ; I find, however, I was anticipated by Professor T. H. Morgan 

 (Science, xxii., 1905). 



