98 THE BIOLOGY OF TWINS 



the external and internal genitalia of a considerable 

 number of freemartins and shows clearly that they 

 range from only slightly abnormal female types, in which 

 the development of the female organs is merely retarded 

 or juvenile in condition, up to those which appear to 

 have developed certain positive male characters, such 

 as testes. Numan's data are extensive and valuable, 

 but his interpretations are open to question. 



Spiegelberg^ (1861) was the next investigator to 

 take up the problem of the freemartin. After a careful 

 study of Hunter's and Numan's works he secured and 

 examined on his own account two cases of full-term 

 twins, giving a detailed description of the gross and 

 microscopic anatomy of all significant parts. His con- 

 clusion was that the freemartin is not an imperfect or 

 sterile female, but an imperfect male. 



Hart^ gives a summary of freemartin literature, 

 drawing largely from Numan's and Spiegelberg's data. 

 His own conclusions are totally erroneous. He was 

 able to make microscopic sections of the gonads of 

 Hunter's freemartins that had been preserved in the 

 British Museum. In each case they appeared to him 

 to have the histological structure of testicular tissue. 

 On the basis of this evidence, taken with other data 

 previously presented, he says: "It seems to me, there- 

 fore, fully established that the freemartin, when the 

 co-twin of a potent male, is a sterile male and not a 

 sterile female: i.e., they are identical twins except in 

 their genital tract and secondary sexual characters." 



' O. Spiegelberg, Zisch. fur rationalle Medicin, Henle and Pfeufer, 

 Drt. Reihe, Bd. XI (1861). 



"D. Berry Hart, Proc. Royal Soc. Edin., XXX (1910). 



