248 THE THEORY OF THE GENE 



tological examination that well-developed testicular-like 

 organs are present in older free martins, i.e., that the 

 characteristic tubular structure of the testes, including 

 rete tubules, sexual cords, and epididymis, is present. 

 Chapin (1917) and Willier (1921) have confirmed these 

 observations, and the latter especially has given a de- 

 tailed account of the transformation of the "indifferent 

 stage" of the ovary into a testis-like structure. 



Magnussen (who erroneously believed the free martin 

 to be a male) found no spermatozoa in the "testes." 

 Their absence he believed to be due to the retention of 

 the testes within the body cavity (cryptorchidism). It is 

 known that in those mammals in which the testes nor- 

 mally descend into the scrotal sacs, sperm-cells are absent 

 when the testes are retained, but in the early embryo 

 germ-cells appear while the testes are still within the 

 body cavity. In the free martin there are, according to 

 Willier, no primordial germ-cells present in the so-called 

 testis. 



Lillie's conclusion that the free martin is a female 

 whose gonads have been transformed into a testis-like 

 organ is so strongly supported by this evidence that it 

 can scarcely be questioned, but whether the effect is to be 

 referred to the composition of the blood of the male, or, 

 as he thinks, to an ovarian hormone in the blood is open 

 to question, since there is at present no evidence of any 

 specific substance produced by the gonad of the male 

 embryo that produces such an effect on the development 

 of the young ovary. Since all the tissues of the male 

 embryo have the male chromosomal composition, the 

 blood may likewise have a different chemical constitution 

 from that of the female, and affect, in consequence, the 

 development of the gonad. It is generally recognized that 

 the young gonads have rudiments of both ovary and testes 

 present, or, as Willier puts it, "the primordium of each 



