50 INTERNAL SECRETIONS 



Van Oordt (1921) has recorded similar facts about the purple 

 sandpiper (Limieola) of Spitzbergen ; the male is much less 

 conspicuously coloured than the female, the male becomes 

 broody, protects the young, and keeps them warm; the male 

 ''behaves like the female of other birds." 



All these details, which at first seem so be of no general 

 interest, are of a great theoretical significance in connection 

 with the problem of the influence of the sexual glands on the 

 organism. Here we have instances which show the relation 

 of this problem to genetics and evolutionary history. Some of 

 the questions might be studied experimentally by means of 

 castration, as has already been done in so successful a manner 

 by Morgan on the Sebright breed, and by the implantation 

 of the sexual glands of other species. How many problems 

 arise in connection with the experiments of Morgan on the 

 Sebright race! Darwin's theory of sexual selection loses much 

 in the light of these experiments. It is possible and even 

 probable that the subdued plumage of the female is genetically 

 more recent than the bright plumage of the male ! 



Two different questions now arise in any discussion on the 

 genetics of sexual characters : how far the somatic psycho-sexual 

 reactions are due to a difference in the sexual gland, and how 

 far are they due to a difference in the somatic substratum itself. 

 In this connection it may be observed that for the Sebright race 

 Morgan showed that the hen-feathering of the male is due to 

 dominant inherited factors phenotypically localized in the 

 sexual gland. 



In discussing such problems one must not forget that the 

 plumage is not an indivisible unity. We have seen that the 

 different parts of the skeleton are not all influenced in the same 

 manner by the sexual glands; a similar statement may be made 

 about the different feathers in birds. We have seen further 

 that the sexual glands can act in different ways ; they can act 

 by furthering and also by inhibiting growth, or, as Pezard says, 

 their actions may be either positive or negative ones. It seems 

 fair to suggest that the type of an adult male or female is the 

 result of an harmonious development of the different parts 

 of an asexual soma, which have been stimulated or inhibited 

 by the sexual glands, or else have not been influenced by the 

 sexual glands at all. In Chapter XL we shall discuss some 

 of these questions more fully. It should be observed, however. 



