DETERMINATION OF SEX IN AMPHIBIANS. 1 33 



individuals whose sex I have ascertained during the course of the 

 experiments which I have made to study the problem of sex- 

 determination in this form. No very definite conclusions can be 

 drawn from the results of the experiments summarized in Table I. 

 The percentage of females obtained from the lot of eggs that was 

 fertilized at a temperature of 26° C, although higher than the 

 probable average for the species, is still within the limits of pos- 

 sible normal variation in the proportion of females developing 

 from eggs laid by different individuals. A relatively low per- 

 centage of females developed from the lot of eggs that was 

 fertilized at 9° C, yet this percentage is about the same as that 

 obtained in one of the series of experiments made to ascertain 

 the influence of nutrition on the determination of sex in Bufa 

 (King, 4). It may be possible to explain the results obtained in 

 this last series of experiments, as well as those of the first series 

 of temperature experiments briefly described above, as due to 

 the fact that occasionally a batch of eggs gives an unusually 

 low or an unusually high percentage of females and that by chance 

 such exceptional lots of eggs were used for these experiments. 



As this last series of experiments was carried out it is open 

 to serious criticism. The eggs that were fertilized in warm water 

 were laid by one female, while those that were fertilized in the 

 cold water were laid by another individual. This gives an op- 

 portunity for the results to be influenced by possible normal 

 variations in the sex-ratios of different lots of eggs. The two sets 

 of eggs were fertilized by sperm from different males also and, as 

 Morgan (8) has pointed out, there is the possibility that the male 

 is responsible for the determination of sex in amphibians. 



In order to avoid all obvious sources of error and, if possible, 

 to obtain results that would give definite conclusions, another 

 series of experiments was made this past spring with the eggs of 

 Bufo. On April 7, 1909, a female which had just begun to lay 

 was killed by pithing and the eggs removed to a dish of fresh 

 water. Lots of about 350 eggs each were artificially fertiHzed 

 in water which was kept at given temperatures (35° C, 30° C, 

 20° C, 10° C, 5° C.) for twenty minutes and then allowed to come 

 gradually to the room temperature (18° C). In all cases sperm 

 from the same male was used. The extreme temperatures at 



