36 HELEN DEAN KING. 



sarily a female. Reed gives no statistics regarding the working 

 out of this hypothesis, but he states that it holds good for a score 

 or more of cases in man and a number of cases in the breeding of 

 horses and cattle. He does not- explain, however, how the theory 

 works in the case of such animals as dogs, pigs, rats, etc., which 

 produce a number of offspring of both sexes at one birth. It can 

 hardly be supposed that the fertilization of the ova in all of these 

 animals invariably takes place "at the turn of the tide" when, 

 according to this theory it might be possible for some of the ova 

 to be fertilized during the positive (male) period and others during 

 the negative (female) period. 



An opportunity was offered to test this theory for Bnfo with 

 the lot of eggs used for the first experiment described in this 

 section. On March 30, 1907, the tide was high at Philadelphia, 

 where the experiments were being carried on, at 2.22 P. M. Ac- 

 cording to Reed's theory the six hours previous to this time woud 

 form the positive period during which all eggs fertilized should 

 develop into males. Of the eggs used for the experiment in 

 questidn Lots A, B and C were laid and fertilized within the pos- 

 itive period and should, therefore, all have become males. Lot 

 D, which was laid about the time of the turning of the tide, might 

 be supposed to produce some females. This last lot, as a matter 

 of fact, did not produce as great a proportion of females as did 

 Lot B, which was laid at the middle of the positive period and 

 therefore, according to Reed, at the most favorable time for the 

 production of males. Results similar to these were obtained with 

 another lot of eggs laid within the positive period. Reed's hy- 

 pothesis, therefore, is not adequate to explain the determination 

 of sex in Bnfo however valuable it may prove to be as a theory of 

 sex-determination in some of the higher mammals. 



IV. THE INFLUENCE OF TEMPERATURE ON THE DETER- 

 MINATION OF SEX IN BUFO. 



It has been held by several investigators that temperature has a 

 decided influence on sex-determination ; a high temperature favor- 

 ing the development of females, a low temperature tending towards 

 male production. Most of the experiments which have seemed 

 to give support to this hypothesis have been carried out with the 



