F. A. E. Crew 175 



encountered, the gonads were either ovary or testis or else the tissues 

 were too undifferentiated to allow of a decision being made. In all 2850 

 tadpoles and frogs were examined. 



But of the frogs which resulted from the union of the male with the 

 abnormal reproductive system and a normal female, every one of the 

 774 examined and found with gonads sufficiently developed was a female 

 normal in every respect. Those of the control lots were typically male or 

 female and no case of abnormality was met with among them. The re- 

 lative numbers of males and females varied in the different lots but 

 only to a slight degree, the average being 4G 7o males, 54 7o females. 

 The average of all the lots was 28 °/^ males and 77 "/^ females, which 

 was distinctly different from the figures of the parental generation 

 (80 °/^ males and 20 °/^ females), constituting, in fact, a very complete 

 swing-back. 



The results of this breeding experiment go far to prove that the 

 male parent was a " somatic " male, a masculinized female. Though 

 possessing the male organisation yet in chromosome-constitution it was 

 a female {XX), and when mated to a normal female {XX) produced a 

 generation consisting entirely of females. Its chromosome-constitution 

 had become over-ridden by external factors. 



There is considerable evidence, as Huxley recently has shown, that 

 chromosome-constitution may thus become over-ridden. He cites the 

 work of Goklschmidt who lately has bred from ZW males and from 

 ■^-^ females of Lymantria, nnd that of Shu 11, Strasburger, and Doncaster 

 on Lychnis dioica. 



Lillie's work on the free-martin can be interpreted as further proof 

 that in the female — presumably XX in chromosome-constitution — 

 embryos in cattle, co-twins of males, the whole organisation can be so 

 altered that even the gonad itself takes on the characters of testis and 

 the accessory sexual apparatus becomes more male than female. 



Doncaster in one of his latest papers suggested that the sterile 

 tortoiseshell tom-cat possibly is a female chromosomally which becomes 

 transformed into an individual with an almost complete male 

 organisation. 



It is generally accepted that the agent responsible for the actual 

 transformation of the gonads is the internal secretion of the testis — the 

 male hormone. It may be assumed that the external factors which are 

 primarily responsible for the reversal of sex act through the medium of 

 the ductless glands. 



Lillie found that twins of cattle are derived exclusively from 



