426 THE GERM-PLASM 



of blue pigeons, for instance, a bird with a white head is paired 

 with another possessing a white tail, and in this way some 

 young may be obtained with white heads and tails. The 

 ' qualtities ' of the white head and white tail are here, therefore, 

 combined. The feathers of both parts of the body, however, 

 have their own determinants ; and in this cross the process 

 which took place in the idioplasm was not the accumulation of 

 homologous determinants, but the acquisition of a majority by 

 the ' white ' determinants for the feathers of the head and tail 

 over the 'blue' ones. This is, therefore, not a case of the 

 summation of like with like, but a victory of similar deter- 

 minants in different parts of the body. 



Surprise has often been expressed at the case, mentioned by 

 Darwin, of two crested canaries which produced young none of 

 which possessed larger crests, while many, at any rate, were 

 bald. As Darwin himself pointed out, the crest in birds is due 

 to a sparser covering of feathers on the head, and this peculiarity 

 may be increased so as to result in baldness in the offspring. 

 This is also an instance of the increase of a ' quality,' but only 

 that of baldness, and not of the crest which is valued by the 

 breeder. In terms of the idioplasm, this may be explained in 

 the same way as was done with regard to the increase of the 

 character of whiteness in pigeons. It is due to the arrangement 

 of ' bald ' determinants, — if I may use such an expression, — 

 some of which are derived from the father and control the 

 region a, the others from the mother controlling the region b. 

 In the father the region h, and in the mother the region a, 

 still possessed a 'feather' determinant; in the offspring the 

 ' bald ' determinants for both regions were accidently brought 

 together owing to the reducing division and the subsequent 

 amphimixis. It is shown by our theory that bald-headed 

 offspring need not invariably result in such a case ; and, as 

 a matter of fact, all the young birds did not exhibit this pecul- 

 iarity. 



The increase in the number of feathers in any particular part, 

 such as has occurred, for instance, in a fantail pigeon, is another 

 case of this kind. The tail of this bird consists of about forty 

 quill-feathers, instead of twelve, as in the original form ; and the 

 breed has undoubtedly been produced by artificial selection, 

 those pigeons always being chosen for breeding purposes which 

 possessed an extra feather in the tail. The young frequently, 



