STUDIES ON SEX-DETERMINATION IN AMPHIBIANS. 221 



The percentage of females among the individuals that developed 

 from the eggs that were subjected to the action of the salt solu- 

 tion before fertilization is greater than that in the lot where 

 a sugar solution had been used. The difference between the 

 two is only 2.52 per cent., however, so it is evident that the 

 sugar solution had practically as great an effect on the eggs 

 as had the salt solution, in spite of the fact that the latter 

 solution has much the higher osmotic pressure. 



Although the methods employed to bring about a change in 

 the water contents of the egg at the time of fertilization were 

 very different in the two sets of experiments just described, 

 there is a very striking uniformity in the results. Both series, 

 comprising five lots of eggs from three different females, show a 

 percentage of females much above the upper limit of the range 

 which is apparently normal for the species and which in three 

 instances is nearly 20 per cent, greater than that in the control. 

 These results suggest, although they by no means prove, that 

 extracting water from the egg at the time of fertilization, or 

 preventing the absorption of water by the egg during this period , 

 in some way affects the sex-determining process and tends to 

 the production of relatively more females. 



The manner in which the experiments were made, particu- 

 larly those in series B, seem to preclude the possibility that the 

 spermatozoa and not the eggs could have been affected by the 

 conditions under which fertilization occurred. The results 

 obtained suggest also that the sex-determining mechanism is 

 in the egg and that it can be influenced by external agencies 

 acting during the fertilization period. 



II. The Effects of the Absorption of Water by the Egg at the 



Time of Fertilization. 



In connection with the experiments just described it seemed 

 worth while to ascertain whether any alteration in the sex ratio 

 of Bufo could be induced by subjecting eggs at the time of 

 fertilization to conditions that would tend to cause them to take 

 up more than the normal amount of water. An increase in the 

 amount of water absorbed could presumably be brought about 

 by fertilizing the eggs in solutions of acid or of alkali, since, 



