174 Sex-Reversal in Frogs and Toads 



tion. But these transformed individuals not only assume the male 

 characters but also can behave and function as males. 



The opportunity neglected by Cerruti (Case 33), of applying the 

 test of breeding in order to examine the exact nature of an individual 

 with an abnormal reproductive system, presented itself to me. 



It can be assumed that in the frog sex-determination is effected by 

 means of a sex-chromosome mechanism. The sex-chromosomes have not 

 yet been demonstrated, but Huxley has given reasons for the belief that 

 the chromosome-constitution of the frog is of the A'^ Y, XX type. 



It so happened that the specimen referred to in the lists as No. 14, 

 when received, was actually in copulation. This pair, with many others, 

 was retained for breeding purposes. The individuals were marked and 

 full details collected during the course of the breeding. Later, when the 

 tadpoles had hatched, the parents were killed and dissected. Then it 

 was that the abnormalities were first noticed and in consequence every 

 attention was paid to the examination of the female with which this 

 abnormal individual had mated and to the rearing of the offspring. The 

 female proved to be normal in every way anatomically ; she died before 

 she could be bred from again. 



The eggs and tadpoles resulting from this union were raised accord- 

 ing to the directions given by H. D. King and every effort made to rear 

 as many individuals as possible. The fertilised eggs from seven other 

 couples were kept under exactly similar conditions to furnish controls. 



The eggs nearer the centre of the egg-mass gave rise to few tadpoles 

 and the eggs that were fertilised did not all hatch, for numbers of such 

 were arrested in their development by death. The question of selective 

 mortality naturally enters into a consideration of the sex-ratio of the 

 individuals which did survive therefore. But there is no evidence to 

 show that the sex-ratio would have been different if every Q^g had 

 hatched and every tadpole had survived. 



As the tadpoles passed the metamorphosis, they were removed to 

 outdoor pens under conditions as natural as possible, the different lots 

 being kept separate. 



During twelve months, the frogs were examined in batches at in- 

 tervals of two months. Every one that died was examined and included 

 in the records. The controls showed no great variation in the relative 

 numbers of the sexes and towards the end of the experiment only two 

 lots were maintained. 



The gonads were sectioned and compared to the standards given by 

 Witschi. No case of the indirect method of development of a testis was 



