THE TESTICLE AND THE OVARY 337 



of North and South Africa as well as the rich dark blue of the 

 southern variety are dependent- upon the presence of the testes, but 

 that the castrated cock attains the normal black plumage which 

 distinguishes it from the hen.^ 



Further evidence that the testis produces an internal secretion 

 is supplied by Nussbaum ^ as a result of his experiments upon frogs. 

 At the approach of the breeding season there is formed in the male 

 frog a thickened pad of skin on the first digit of each fore limb 

 associated with an increased muscular development in the fore arm. 

 This modification is preparatory to the act of copulation, when the 

 male frog uses its arms in embracing the female, and so assists in 

 pressing out the eggs from the oviduct (see p. 20). If t^e male frog 

 be castrated, the pad is not formed and the muscles fail to develop. 

 Nussbaum found that, if pieces of testis from another frog were 

 grafted into the dorsal lymph sac of a frog previously, castrated, the 

 secondary sexual characters of the latter developed just as in a 

 normal frog. The transplanted testes, however, after exerting their 

 influence in the way described, underwent a gradual absorption. 



Nussbaum stated, further, that when the nerves supplying the 

 first digit were severed, the pad did not develop, this operation being 

 performed on a normal frog. Similarly if the nerves supplying the 

 clasping muscle of the fore arm were severed, the enlargement did 

 not occur. He concluded, therefore, that the internal secretion 

 formed in the testis had a specific action upon certain local groups 

 of ganglion cells, and that the nerves passing from these to the fore 

 arm and digit convey a stimulus which induces the growth of the 

 muscle and that of the thickened pad. In support of the view that 

 the testis exerts its influence upon the metabolism (at least partially) 

 through the medium of the nervous system, Nussbaum cites an 

 observation of Weber, according to whom an hermaphrodite finch, 

 having an ovary on one side of the body and a testis on the other, 

 showed the characteristic female coloration on the ovarian side and 

 the male plumage on the side of the testis. 



Nussbaum's conclusion has been controverted by Pfluger,* who 

 points out that in other cases the apparent effect of section of nerves 

 is due to loss of sensibility in the parts affected, in consequence of 

 which the tissues are not guarded from injury, and further, that the 



' Duerden, " Crossing the North African and South African .Ostrich," Joiir. 

 of Genetics, vol. viii., 1919. The akin of the hen and young bird of both sexes 

 is grey. Spayed hens assume the black plumage of the cock (see below, p. 344). 

 Of. Fitzsimons, "A Hen Ostrich with the Plumage of aCock," Agric. Jow. 

 University of South Afi-ica, vol. iv., 1912. 



^ Nussbaum, "Innere Sekretion und Nerveneinfluss,'' Merkel and Bmvnet, 

 Ergeh. der Anat. und Entwick., vol. xv., 1905. 



^ Pfluger, " Ob die Entwicklung der sekundaren Geschlechts-charaktere vom 

 Nervensystem abhangt?" PflUger's Arch., vol. cxvi., 1907. 



