46 LEO LOEB. 



testicle and epididymis in the guinea pig. The interstitial cells 

 are developed to an extraordinary extent. The organs were cut 

 in complete serial sections and no trace of ovarian structure was 

 found. From the descriptionsgiven by Miss Chapin, I should judge 

 that a similar condition has not been observed in the fetal gonads 

 of the freemartins. In the guinea pig, uterus and vagina as well 

 as vas deferens, seminal vesicles and penis were absent. While 

 I was unable to find a description of the histology of the mammary 

 gland in freemartins, we observed in our case a typical female 

 mammary gland with the added peculiarity that the mammary 

 glands of both sides were unequal. 



The question arises, whether the guinea pig which we observed 

 was an analogue to the freemartin in cattle. Was this animal 

 originally the twin sister of a brother, under whose influence the 

 observed deficiencies were produced? While we cannot defi- 

 nitely exclude such a possibility we must consider the fact that 

 neither ourselves nor anyone else has so far observed twins with a 

 coromon chorion and deficiencies in the development of the sexual 

 organs in rodents. Lillie himself points out the great improba- 

 bility of such an occurrence in animals in which the ova enter 

 the uterine wall at an early date and in which the uterine horns 

 are separated. On the other hand, we accidentally observed in 

 several cases absence of one uterine horn in guinea pigs. Mal- 

 formations of the sexual organs do therefore occur. It is very 

 probable that similar malformations may be due to different 

 interferences in the embryo, just as we know that cyclopic con- 

 ditions of the eye can be produced in different ways. We inter- 

 preted in our paper the conditions which we found in the guinea 

 pig as consisting essentially in the presence of an abnormal, in- 

 completely developed male gonad in which generative cells are 

 absent, and in which the interstitial cells show an unusually 

 pronounced development. This maleness of the gonad and 

 especially the marked development of an interstitial gland is 

 associated with deficiencies in the formation of the efferent genital 

 ducts and with a female mammary gland. We interpreted this 

 unusual condition as due to the original female constitution in 

 the animal, to the tendencies toward femaleness which prevented 

 the male interstitial cells from exerting their specific influences 



