SEXUAL HORMONES AND MORPHOGENESIS 463 



We see that the males of the first generation are similar in 

 both experiments, whereas the females have the plumage of 

 the male parent (sex-limited inheritance). To explain this 

 result the authors assume that the ovary in the F^ generation 

 of A checks the development of the plumage of the neutral 

 Dorking form, and changes the plumage of the neutral Leghorn 

 form into a female one ; the result is pure Leghorn plumage in 

 the Fi hens in A and vice versa a plumage of pure Dorking in 

 the Fj hens in B. The acceptance of this theory of Pezard and 

 Caridroit that the ovary is able to exercise a special influence 

 besides its general sex specific influence might be controlled 

 by castration experiments. If Pezard and Caridroit are right, 

 castration of a hen of the generation F^ in A and B should give 

 the same result : a plumage presenting a mixture of characters 

 of Leghorn and Dorking; if such a castration experiment were 

 to result in the plumage of a capon of a pure Leghorn male in A 

 and the plumage of a capon of a pure Dorking male in B, it 

 would be necessary to reject the theory. Cuenot points out 

 that certain experimental facts are in harmony with the 

 presumption that the result of the indicated castration experi- 

 ments would be pure Leghorn and pure Dorking plumage; he 

 mentions an experiment of Davenport (1912), in which a male 

 golden Leghorn was mated with a female dark Brahma. In the 

 Fj generation there were cocks with characters of both parents, 

 whereas the hens were of the type of golden Leghorn. In the 

 F2 generation there were cocks with mixed characters as well 

 as male birds of the pure Leghorn type. 



That the sex hormones, however, may differ according to the 

 species is not improbable, and this may be the explanation of 

 many facts. We shall return to this question in Section H. 

 In Chapter II. we have already touched on its importance in 

 relation to phylogenetic problems. Pezard (1918, p. 173) 

 pointed out that a factor responsible for evolution might have 

 acted primarily on an endocrine gland which had a morpho- 

 genetic influence on the whole organism. Morgan's experi- 

 ments (1919) may be especially referred to in this connection. 

 We know that a peculiarity so characteristic of a given race as 

 the hen-feathering in the Sebright is probably caused by an 

 hormonic factor. Here the introduction of a single factor 

 seems to produce manifold changes, or, as Morgan says, "a 

 single factorial difference may be at the root of exceedingly great 



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