F. A. E. Crew 179 



original population including 80 7^ males. All (774) of his offspring 

 which attained a sufficient development to permit identification of the 

 sex were females. Including these 774 females, the tadpoles produced 

 from the original population were 23 7o males and 77 7„ females. 



4. This " swing-back " is taken as evidence which supports the con- 

 ception that the frog has a chromosome constitution of the XV, 

 XX type, and that these cases of abnormality are females {XX), the 

 chromosome constitution of which has become over-ridden by external 

 factors, and which are " somatic " males or masculinised females. These, 

 being XX in chromosome-constitution, mating with normal females, also 

 XX in constitution, will produce a generation consisting entirely of 

 females. The presence of such "somatic " males in a population will 

 thoroughly disturb the sex-ratio of the succeeding generation, producing 

 a " swing-back " which is a certain indication of their presence and re- 

 productive activities. 



o. The mechanism by which the individual is thus transformed is 

 one which acts through the internal secretions of the gonads. It is 

 shown that in the frog the phenomenon of sex-reversal is very similar 

 to the same process in cattle save that in the frog there is an antagonism 

 of the sex-hormones and that the ovarian is powerless in the presence 

 of the spermatic. 



6. It is shown that there is a most intimate relation between the 

 primary sex-glands and the accessory sexual apparatus and the 

 secondary sexual characters. 



7. Reasons are given for questioning the generally accepted opinion 

 that Bidder's organ is a rudimentary ovary. 



Since the present writer first offered a, suggestion as to the possible significance 

 of the abnormalities in frogs, an important contribution to the literature dealing 

 with the subject of reversal of the sex-organisation has been made by Champy, C. 

 (C. R. Acad. Set. Paris, Seance du 9 Mai, 1921.) 



Champy had previously observed that the annual incidence of spermatogenesis 

 in Tritons could be prevented by starvation, and that in males, killed in Spring 

 after such treatment, the testicles had become replaced by fat which contained 

 groups of undifferentiated gonocytes. 



More recently he found that two such males when fed intensively began to 

 assume the external characters of the female. One was killed for examination and 

 the gonad was found to have been replaced by fat as in the previous cases. The 

 other specimen was kept alive for further observation. Its history was known ; it 

 had been a perfect and complete male, and had fertilised the eggs of a normal 

 female. Gradually it came to be exactly like a female in appearance. It was ulti- 

 mately killed. On examination each testis was found to have been replaced by a wide 

 Journ. of Gen. xi 12 



