STUDIES ON SEX-DETERMINATION IN AMPHIBIANS. 2IQ 



not fertilized at all after being subjected to the action of solutions 

 of different strengths for varying lengths of time, or practically 

 all of the eggs that segmented died during the early stages of 

 development. The unfertilized eggs of Bufo, as well as those of 

 Rana according to the investigations of Hertwig ('95), are very 

 sensitive to the action of hypertonic solutions. It was necessary, 

 therefore, to make other experiments this past spring in order 

 to ascertain the maximum strength of solutions that could be 

 employed and the length of time they could act without injuring 

 the eggs beyond the possibility of their being fertilized and con- 

 tinuing their normal development. The experiments from which 

 results were finally obtained were made as follows : a batch of ripe 

 eggs was transferred directly from the uterus of a female into a 

 2.5 per cent, solution of c.p. cane sugar and allowed to remain there 

 for ten minutes. During this time the eggs were kept in constant 

 motion, either by stirring them with a glass rod or by gently 

 shaking the dish. The eggs were then placed in a small amount 

 of tap water containing a quantity of spermatozoa. A second lot 

 of eggs from the same female were subjected to the action of a 

 2.5 per cent, solution of c.p. sodium chloride for the same length 

 of time and were then fertilized with spermatozoa from the male 

 used in the previous case. 



Even with the weak solution that was used and for the short 

 time that it acted many of the eggs that had been put in the sugar 

 solution were killed, or at least rendered incapable of being 

 fertilized; not more than one half of the eggs subjected to the 

 action of the NaCl segmented, and many of these did not go 

 beyond the gastrulation stage. Morgan ('06) has shown that 

 the fertilized eggs of the frog can develop normally in a 6 per 

 cent, solution of cane sugar, but that the maximum strength of 

 NaCl that will permit of normal development is not much above 

 2 per cent. The more injurious action of the NaCl on the 

 eggs of the frog, as well as on those of the toad, is doubtless 

 due, in great part, to the fact that its osmotic pressure is several 

 times greater than that of sugar. 



As the unfertilized eggs of Bufo are so quickly injured by 

 solutions of salt and of sugar it is difficult to decide what effects 

 these solutions could have had in the short time the eggs remained 



