MUTATION. 153 



lighter coloured than the females. The ideal animal is uni- 

 formly marked all over, and every feather must be white, set 

 off with a narrow, but uninterrupted black border. In animals 

 which are too dark, the black border encroaches upon the 

 white centre, and in extreme instances the feathers become 

 black with a narrow whitcish streak along the shaft. On the 

 other hand, in animals which are too Ught, the feathers may 

 become almost white, with a small black tip. The standard 

 of perfection of this breed of fowls calls for a marking of the 

 feathers equal in both sexes. Now it has been found in prac- 

 tice, that it is impossible to establish a family of Silver Wy- 

 andottes, in which perfectly marked cocks are regularly pro- 

 duced, as well as hens which come up to the standard of 

 perfection. As the males have a tendency to be lighter marked 

 than the females, the SiverWyandotte as it is exhibited in 

 poultry shows, consists of two distinct species, a male-pro- 

 ducing strain, and a strain which furnishes exhibition hens. 

 Some fanciers breed both species, and others specialize in 

 one of them, and strive either to produce prize-winning cocks 

 or perfect hens. The cocks, in the species which produces well- 

 marked hens, are very light, and reversely, the hens in the 

 strain which is kept for the production of good males, are too 

 black to be able to compete in the shows. Here the number of 

 genes which influence the shade of the birds must be larger 

 than one, for there are families of Silver Wyandottes, of which 

 the members are far lighter than even the hen-breeding strain, 

 so light, that the cocks are whiteish and the hens even are much 

 too light. And also, there are strains of SUver Wyandottes of 

 which even the males are too black. The difference in shade 

 between the sexes in every family must ultimately depend 

 upon the genotypic difference, which makes some animals be 

 hens and others males. In many species of chickens a similar 

 difference exists, e. g. in Barred Pljmiouth Rocks. 



If it were true that the loss of a gene might result in the pro- 

 duction of a new form, dominant in the quahty affected by 

 this gene, over the form from which it was derived, it would be 



