THE GENERATIVE GLANDS 369 



period, but that those of the sound side hypertrophied as usual. 

 He concludes from this that the testicular secretion stimulates 

 certain nervous centres and certain groups of ganglia only, and 

 that these produce, by means of centrifugal nerves, changes in 

 the form and the metabolism of the organs innervated by them. 

 It is not possible to adopt this assumption without further proof, 

 however. As Pfliiger points out, the arrest of the motility and 

 sensibility of the vaso-motor and secretory nerves produced by 

 resection, is sufficient in itself to account for the absence of hyper- 

 trophy. It is superfluous, at the very least, to assume that the 

 internal secretion of the genital gland produces its effect, not 

 directly, but by the agency of the nervous system. 



In man, the secondary sex characteristics attain their full 

 development at puberty, that is to say, at a time when the genital 

 glands are fully developed, and the individual has attained to 

 sexual maturity. It is apparent, from what has gone before, that 

 the beginnings of the somatic sex characteristics are largely 

 present in the embryo, and that, like other tissues, they continue 

 to develop from birth until puberty. 



It is a remarkable fact, however, and one which points to an 

 intimate association of the sex stigmata with the genital glands, 

 that several of the attributes of sex do not make their appearance 

 until the maturity of the genital glands is proclaimed by the 

 development of their external secretory processes (spermato- 

 genesis, menstruation, ovulation). The maturity of the secretory 

 function of the genital glands is shown, in boys, by a slight 

 enlargement of the testicle. In girls, it is expressed by the 

 menstrual haemorrhage which accompanies ovulation, that is, the 

 expulsion of the ovum ready for fertilization. Many of the 

 changes of puberty are common to both sexes ; such are the rapid 

 skeletal growth and the appearance of hair at the pubes and the 

 axilla? ; others, such as the growth of hair on the face, the altera- 

 tion in the voice, and the appearance of hairs all over the body, 

 are peculiar to the male; while others again, such as the develop- 

 ment of the mammary glands, the peculiar pelvic formation, and 

 the deposition of fat in certain localities are essentially feminine. 



Among the secondary sex characteristics which make their 

 appearance at puberty, are those reflex nervous mechanisms which 

 are concerned in the performance of the sexual act. Through the 

 agency of the internal secretion of the genital glands, the 

 apparently low nerve centres which are here concerned acquire 

 a specific sensibility. Goltz showed that, during the spawning 

 season, the male frog reacts to every touch upon the skin of the 

 chest with the embracing reflex, and that this reflex may still be 

 obtained shortly after removal of the testicles and even after 

 decapitation. That the increase in reflex sensibility is not general, 

 is proved by the fact that the muscle-contractions are not obtained 

 in response to every kind of touch, but are only provoked by the 



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