2l6 HELEN DEAN KING. 



3. THE EFFECTS OF CHANGING THE WATER CONTENT OF THE 



EGG AT THE TIME OF FERTILIZATION ON THE SEX 



RATIO OF Bufo lentiginosus. 



I. Extracting Water from an Egg, or Preventing the Absorption 

 of Water by an Egg, during the Fertilization Period. 



If the sex of an embryo is definitely fixed at the time that 

 the egg is fertilized, it is conceivable that the sex-determining 

 process may be of such a character, and so evenly regulated, that 

 placing the egg under conditions that would cause it to lose 

 water or that would prevent its absorption of water during the 

 fertilization period might turn the balance in favor of one sex 

 or the other. Normally, as shown by the investigations of 

 Backman and Runnstrom ('09), the osmotic pressure of the 

 ovarian egg of Rana, and presumably also that of Bufo, drops 

 from .48 to .045 when the egg has been fertilized but is still 

 unsegmented. This lowering of the osmotic pressure must 

 be due in great part to the absorption of water by the egg as 

 Bialaszewicz ('08) has recently maintained, although the change 

 is ascribed by Backman and Runnstrom chiefly to an alteration 

 in the condition of the colloids that is induced by fertilization. 

 Any cause that would tend to prevent the normal increa c e in 

 the water content of the egg at the time of fertilization might, 

 therefore, produce changes that would be far reaching in their 

 results. 



In attempting to ascertain whether extracting water from the 

 egg, or preventing the egg from absorbing water during the fertili- 

 zation period, would produce any alteration in the sex ratio, 

 two different methods of investigation were employed. For 

 convenience in description these two sets of experiments will be 

 designated as series A and series B. 



Series A. -While making experiments with the eggs of Bufo 

 in the spring of 1909, a pair of toads was placed in an empty 

 aquarium and left undisturbed for several hours. During this 

 time the female laid a small batch of eggs which were found to 

 be segmenting when the toads were removed from the aquarium 

 for use. The eggs which had thus been normally fertilized out 

 of water were placed at once in a dish of tap water and allowed to 



