STUDIES ON SEX-DETERMINATION IN AMPHIBIANS. 22Q 



of females obtained in the other two lots. In the total of 246 

 individuals in this series in which sex was ascertained 126 were 

 females. The proportion of females in this series is therefore 

 51.21 per cent., which is remarkably close to that in the control 

 lot (51.41 per cent.). 



In none of these experiments does the observed percentage of 

 females differ in any great degree from that of the control. The 

 results therefore agree very well with those of the other series in 

 which eggs were fertilized in solutions of NaOH (Table VII.). 

 Since the fertilization of eggs in solutions of NaOH produce no 

 apparent effect on the sex ratio of Bufo, it is evident that either 

 the solutions used were not strong enough to penetrate the egg 

 membranes and act on the egg in the short time in which the 

 eggs remained in them, or that NaOH is not a substance that can 

 act on the egg in such a way as to increase its tendency to pro- 

 duce a male. A further series of experiments will be made in 

 which the eggs are subjected to stronger solutions of NaOH 

 before fertilization. It is probable that the eggs are less readily 

 injured than the spermatozoa by various solutions, and it may be 

 possible to subject them to the action of a comparatively strong 

 solution without serious injury. 



DISCUSSION. 



The possibility that the relative amount of water in the am- 

 phibian egg at the time of fertilization may have some influence 

 in determining sex seems to me to afford a plausible explanation 

 of the unusual sex ratios obtained by Hertwig ('06, '07), and by 

 Kuschakewitsch ('10), in lots of frogs developed from eggs that 

 were overripe when fertilized. In several of his experiments 

 Hertwig obtained from 70-90 per cent, of males; while in one 

 experiment made by Kuschakewitsch, in which the fertilization 

 of a batch of eggs of Rana esculenta was delayed for 89 hours, 

 all of the resulting individuals were males. As the mortality 

 in this last lot was only from 4-6 per cent, it is not possible to 

 explain the results as due to selective mortality. Hertwig at- 

 tributes the great excess of males in these experiments to the 

 "Kernplasmarelation" existing in the eggs at the time that they 

 were fertilized. He believes that young eggs, and also those that 



