x SEX 105 



pure for the grossulariata character this can never happen 

 in a state of nature. 



An essential feature of the case of the currant moth lies 

 in the different results given by reciprocal crosses. Lacti- 

 color female X grossulariata male gives grossulariata alone 

 of both sexes. But grossulariata female X lacticolor male 

 gives only grossulariata males and lacticolor females. Such 

 a difference between reciprocal crosses has also been found 

 in other animals, and the experimental results, though 

 sometimes more complicated, are explicable on the same 

 lines. An interesting case in which three factors are 

 concerned has been recently worked out in poultry. The 

 Silky breed of fowls is characterised among other pecu- 

 liarities by a remarkable abundance of melanic pigment. 

 The skin is dull black, while the comb and wattles are of 

 a deep purple colour contrasting sharply with the white 

 plumage (PL V., 3) . Dissection shows that this black pig- 

 ment is widely spread throughout the body, being espe- 

 cially marked in such membranes as the mesenteries, the 

 periosteum, and the pia mater surrounding the brain. 

 It also occurs in the connective tissues among the muscles. 

 In the Brown Leghorn, on the other hand, this pigment 

 is not found. Reciprocal crosses between these two 

 breeds gave a remarkable difference in result. A cross 

 between the Silky hen and the Brown Leghorn cock pro- 

 duced Fi birds in which both sexes exhibited only traces 

 of the pigment. On casual observation they might have 



