XII] THE MALE GENERATIVE ORGANS 163 



the uncastrated males and so approximate towards horns of the 

 female type. Early castration in deer prevents the development 

 of the antlers. If the operation is performed late only clump or 

 peruke antlers grow, and these tend to persist instead of falling off 

 in the non-breeding season. If castration is done when the antlers 

 have grown, these fall off, and ne.xt season are replaced by peruke 

 antlers. The horn sheath, however, is not shed. In castrated cats 

 the growth of the tissues of the cheek or jowl is partiall}'^ ar- 

 rested. In poultry the complete male plumage is not assumed 

 after cajionisation or removal of the testes, and the comb, sj^urs, 

 etc. are said not to develop to their full extent, but there appears 

 to be a good deal of variation in these results. 



Another result of early castration in both birds and mammals 

 is the arrest in the ossification of the epiphyses, the consequence 

 being that the limb bones groAv larger and that there is a tendency 

 towards giantism such as is associated also with pituitary disease. 

 Again, the thymus gland which normally atrophies at or about 

 puberty persists longer or even hypertrophies in individi;als which 

 have undergone castration. 



Castration is followed also b}^ atrophy of the j^rostate and 

 other accessor}^ male glands, or if the operation is carried out before 

 puberty these do not fully develop and sexual desire and penile 

 erection do net occur, not even on stimulating the nervi erigentes 

 artificially. 



Transplantation of the testes or of portions of these organs to 

 abnormal positions such as the ventral peritoneum or that of the 

 gut (fowls, etc.) notwithstanding that the ordinary nervous con- 

 nections of the testes are destroyed, does not arrest the growth 

 of the secondary male characters. It would seem clear therefore 

 that the testicular influence is chemical and not nervous, that is 

 to say, that it acts by the internal secretion of substances into 

 the blood, and that these substances are carried in the circulation 

 to the various tissues influenced by them, growth and seasonal 

 activity being thus brought about. 



The further question arises as to what part of the testis is con- 

 cerned in elaborating this internal secretion or hormone. It has 

 already been mentioned that in those animals in which testicular 

 transplantation to abnormal positions had been carried out castra- 

 tion effects did not occur, and this is also true for animals in which 

 the vasa deferentia had been cut. In such experiments, however, 



