SEXUAL HORMONES AND MORPHOGENESIS 451 



and the teats of the male guinea pig are still very similar to 

 those of the female of that age, and it is easy to understand 

 that under these circumstances the reaction of these organs 

 in the feminized male will be similar to that in an ordinary 

 female. On the contrary, the penis in the new-born male 

 guinea pig, and especially in one of 2 to 3 weeks old, is very 

 different from the clitoris of the female of the same age, the 

 corpora cavernosa undergoing sexual differentiation towards 

 maleness or femaleness during embryonic development. For- 

 mation of a normal penis in a masculinized guinea pig of this 

 age is not possible, though male sexual hormones are now in 

 process of circulation. The result is the formation of the 

 hypospadic penis, which is shorter than the normal organ. 



It is very interesting to note that neither Steinach nor Sand 

 nor Moore could discover any effect produced by the ovarian 

 graft on the development of the mammary glands or teats in 

 rats completely feminized in respect of sexual instincts. /. A, 

 Myers (19 16, 19 17 a, 19 17 b) stated that the sexual differentia- 

 tion of the mammary gland in the female rat begins about 

 five weeks after birth. The rudimentary mammary glands in 

 the male and female at ages of about 4 or 5 weeks are already 

 very different from one another; the nipples are wholly absent 

 in the male rat. The young rat, therefore,, is very different 

 from the young guinea pig, in the former there being profound 

 differences between male and female, and in the latter no 

 difference at all. In view of these facts it is possible to explain 

 the different reaction towards the female sexual hormones 

 shown by the two species of rodents in the experiments with 

 cross-grafting of ovaries.^ 



Certain observations of Goodale (1916) and Pezard (1918) 

 deserve to be mentioned here. In fowls sexual differentiation 

 of the plumage takes place at an age of about two months. 

 At this time the plumage characteristic of the two sexes begins 

 to develop. Evidently the inhibitory influence of the female 

 hormones begins to act at this time in the hen and to fix the 

 plumage in a sex specific manner. If the young hen has been 

 castrated at an age of two months, the male plumage does not 

 appear immediately after castration, but much later. In the 



1 Even in fully grown guinea pigs of about i^ years of age the teats and 

 mammary glands can undergo, after ovarian transplantation, hyperfeminiza- 

 tion with milk secretion, as shown by Lipschiilz and Voss (unpublished 

 experiments, see p. 291). 



