132 INTRODUCTION TO SEXUAL PHYSIOLOGY 



over the sexual characters at a time when the ovary is still rudi- 

 mentary ; and lastly, Lillie and Bascom have been able to demon- 

 strate an embryonic interstitial gland in the testis of the bull calf, 

 and it is to this gland that the masculinising influence is ascribed. 

 The free-martin then is an intersexual individual, its condition 

 being determined by a hormone arising from the embryonic 

 testis of its male twin. Keller has demonstrated a similar inter- 

 sexuality in the goat and shown it to be due to chorionic union 

 in the same way as in the cow. 



Minoura states that he has produced intersexual ity experi- 

 mentally in the chick by removing a portion of the egg-shell 

 during the second week of incubation, and grafting on to the 

 vascular area of the chorio-allantoic membrane a portion of a 

 gonad of another bird belonging to the opposite sex. The grafts 

 were taken from birds of all ages, from ten-day chicks to mature 

 birds. During the remainder of the incubation period, after the 

 operation (from six to twelve days), intersexual individuals of 

 all grades were formed. These intersexual chicks are regarded 

 as artificial free-martins, the stimulus for the abnormal sexual 

 development being derived from the transplanted gonad. This 

 explanation has, however, been questioned, and the suggestion 

 made that the abnormalities produced were the result of inter- 

 ference in normal development (Greenwood). 



In view of these experiments and the observations made upon 

 the condition of life of the free-martin, the question arises, why 

 in mammals intersexual individuals are not habitually pro- 

 duced from those which start as males owing to the influence 

 of sexual hormones arising from the ovary of the mother ? No 

 definite answer can be given to this question, but it is suggested 

 that the hormone may be in some way arrested from penetrating 

 through the placenta, which, as we have already seen, apjjears 

 to exercise a selective action over some of the substances which 

 transfuse to the foetus, the maternal and the foetal circulatory 

 systems being always quite distinct, without any union of vessels, 

 such as is found between the chorions of the free-martin and its 

 twin. 



Goldschmidfs Theory of Sex-Determination. — We have seen 

 that the sex of the future individual, in many animals at least, is 

 apparently determined by the chromosome constitution of one 

 or other of the gametes which unite to form the zygote producing 



