The Evidence from Hybrids. 131 





Difficulty of Explaining the Transmission of the Char- 

 acters of Two Forms without Fusion. 



A much more serious difficulty is found in the fact 

 that while a hybrid is usually somewhat intermediate 

 between its parents, it occasionally happens that the 

 characteristics of one or both parents refuse to blend and 

 are transmitted in an unmodified state. Thus Darwin, 

 states that when gray and white mice are paired the 

 young are not piebald nor of an intermediate tint, but 

 are pure white or of the ordinary gray color. This par- 

 ticular case may perhaps be explained as follows : The 

 brown form is the ancestral form, and when no hair 

 gcmmules are transmitted the young are brown. All 

 the hairs are homologous with each other, and are derived 

 from the same part of the egg, and when gemmules are 

 transmitted they may hybridize alike all the cells which 

 are to form hairs, and the hybrid animals will therefore 

 be entirely white or entirely brown. 



It is stated that when a black game fowl is crossed with 

 a white, the young are either pure black or pure white, 

 but this case is precisely like that of the mice. 



Darwin gives a number of interesting illustrations of 

 this singular phenomenon, among which are the follow- 

 ing: 



When turnspit dogs and ancon sheep, both of which 

 have dwarfed limbs, are crossed with common breeds, 

 the offspring are not intermediate in structure, but re- 

 semble one parent only. 



When tailless or hornless animals are crossed with 

 perfect animals, it frequently but by no means invaria- 

 bly happens that the offspring are either perfectly fur- 

 nished with these organs or are quite destitute of them. 



When Dorking fowls with five toes are crossed with 



