2O8 HELEN DEAN KING. 



various series should be known and taken into account in con- 

 sidering the results. With the large numbers of eggs that were 

 necessarily used in these studies it was quite impossible to take 

 the time to make an accurate count of the eggs when the experi- 

 ments were made. For the eggs of the toad, when taken from 

 the uterus, are so closely packed together in long strings of thick 

 jelly-like substance that they are greatly distorted in shape, and 

 a rather careful examination with a lens would be necessary to 

 enable one to tell the exact number of eggs in any given lot. 



It is possible that distinct variations in the sex ratios might 

 be obtained when batches of eggs from different females are 

 fertilized with sperm from different males. A control for each 

 series of experiments was therefore considered necessary, and 

 was obtained by fertilizing eggs from the same female with sperm 

 from the same male in ordinary tap water. The percentage 

 of females in this control lot was taken as the standard by which 

 to judge whether the sex ratio had been altered by the changed 

 environmental conditions to which the particular lot of eggs 

 had been subjected at the time of fertilization. 



i. THE INFLUENCE OF ALCOHOL ON THE SEX RATIO OF Biifo. 



To subject eggs to the action of solutions that would produce 

 marked alterations in the cell structure would seem to be an 

 easy way of ascertaining whether sex can be influenced by ex- 

 ternal conditions acting at the time of fertilization. Unfortu- 

 nately the unfertilized eggs of amphibians, as well as those of 

 the different invertebrates that are extensively used for experi- 

 mental purposes, are very sensitive to the action of various sub- 

 stances, even when used in very dilute solutions for only short 

 periods of time. It is therefore not possible to put the eggs of 

 Bufo in any solution strong enough to greatly modify the cell 

 structure without causing immediate death or inducing changes 

 that prevent normal development. 



Experiments made by Morgan and Tsuda ('93) show that the 

 eggs of the frog, and also those of the toad, can develop normally 

 for some time if they are placed in a 2.5 per cent, solution of 

 alcohol, although they are not able to live in a 5 per cent, solu- 

 tion. As eggs and sperm, according to Overton ('02), are equally 



