ORGANS OF INTERNAL SECRETION 313 



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. 22). If the male frog be castrated, 

 the pad is not formed and the muscles fail to develop. Nuss- 

 baum 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 ab- 

 sorption. 



Nussbaum states, further, that when the nerves supplying 

 the first digit were severed, the pad did not develop, this opera- 

 tion 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 concludes, therefore, that the 

 internal secretion formed in the testis has 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 charac- 

 teristic female coloration on the ovarian side and the male plumage 

 on the side of the testis. 



Nussbaum's conclusion has been controverted by Pfliiger, 1 

 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 con- 

 sequence of which the tissues are not guarded from injury, and 

 further, that the secondary sexual characters of animals are 

 usually arranged symmetrically. The effect produced by one- 

 sided castration is general rather than local, and the operation 

 has little or no influence in destroying the symmetry of the sexual 

 characteristics (cf., however, Fowler's statement about fallow 

 deer, which appears to be exceptional). It is probable, therefore, 



1 Pfliiger, "Ob die Entwicklung der sekundaren Geschlechts-charaktere 

 vom Nervensystem abhangt?" Pjlwje.r'a Archiv, vol. cxvi., 1907. 



