THE STRUCTURE OF FREE-MARTIN GONADS 111 



Not only is there this general correlation between the various 

 parts of the free-martin reproductive system, but the correlation 

 is still closer if the parts on one side are compared. Case 44 

 (table 2) showsala r ge left gonad associated with a large Wolffian 

 duct and a large seminal vesicle, while the right gonad has a 

 smaller duct and a smaller seminal vesicle. Case H-37 shows 

 the left gonad one and a half times larger than the right gonad, 

 and the left seminal vesicle is fairly well developed and possesses 

 a duct which ends blindly, while the right seminal vesicle is 

 poorly developed and its duct entirely absent. Lillie ('17) 

 showed that disturbances in relation of parts in foetal stages are 

 found on the right side, as, for instance, in his case 2 (fig. 20, A) 

 where the gubernaculum on the right side evaginates into the 

 body cavity instead of into the body wall, as the left one does. 

 These lateral variations certainly indicate that physiological 

 factors, other than the action of sex hormones, play a part in 

 correlation. There is some embryological basis for these lateral 

 variations, as is seen from an examination of a number of ovaries, 

 the majority of which are from young calves. In the number 

 examined (20) about 65 per cent show the left ovary to be larger 

 and the follicles more advanced than in the right. 



A very interesting situation is presented if the lateral varia- 

 tions of the reproductive glands of the free-martin are compared 

 with similar variations in other vertebrates. According to 

 Simpson ('36), in the human the left side usually has the female 

 type of gonad and disturbances are usually found on the right 

 side (a number of more recent cases support this observation). 

 Among other groups of vertebrates, lateral variations occur 

 normally where the left ovary is larger and the functional one. 

 The monotremes have a larger left ovary and eggs have been 

 found only in the left oviduct. In birds the right ovary degen- 

 erates and among certain of the skates (Trygon, Myliobatis and 

 relatives) the left ovary alone functions. Although there may 

 be certain mechanical factors which result in the functioning of 

 one ovary, it is certainly no coincidence that it is always the 

 ovary on the left side which is functional. From the above 

 considerations it would appear that some physiological processes 



