4. Fortpflanzuugslehre. 



369 



In these experiments a batch of eggs from the right Uterus of a female 

 was divided into four lots of from 300 — 400 eggs each. Each lot of eggs 

 was tuen fertilized with sperm from the right or left testicle of one of three 

 different raales. The sex ratios are given in Table IL 



The results are negative both as regards the males used and as regards 

 the use of the right or left testicle. 



(3) The Effects of Changing the Water Content of the Egg at the Time 

 of Fertilization on the Sex Ratio of Bufo lentiginosus. 



(1) Extracting Water from an Egg, or Preventing the Absorption of 

 Water during the Fertilization Period. 



In one division of these experiments the eggs were fertilized dry, being 

 placed in water four hours and seven hours respectively after fertilization. 

 The percentage of females was 60,86 and 70,83 respectively. 



In the second series of experiments sugar and salt Solutions were employed 

 in extracting water from the egg. Very weak solutions only could be used 

 without killing the eggs, which were fertilized after exposure to the solutions 

 for ten minutes in fresh water. 



With a 2V3 per cent NaCl Solution the percentage of females was 72,52, 

 and in 2 7 2 P er cent sugar Solution the percentage was 70, considerably higher 

 than that of the control. 



The results suggest that the sex determining mechanism is in the egg 

 and that it can be influenced by external changes acting during the fertili- 

 zation period. 



(2) The Effects of the Absorption of water by the Egg at the Time of 

 Fertilization. 



It was attempted to increase the amount of water absorbed by the egg 

 by fertilizing in acid or alkali. The eggs and sperm were placed together in 

 the Solution and left for one half hour. They were then washed in several 

 changes of fresh water and placed in fresh water. With 0,01 per cent acetic 

 acid the percentage of females produced was 41,77; with 0,0025 per cent the 

 percentage of females was 36,30. In a third experiment with 0,01 per cent 

 acetic acid the percentage of females was 44. Experiments with alkali, on 

 the other hand seemed to tend to produce a slight excess of females above 

 the normal ratio. 



In a later series of experiments with acids the percentage of females 

 was as low as 31,5. With alkali again the ratio was not much different 

 from the normal. 



The author does not maintain that the results from any of these experi- 

 ments are conclusive, but they seem to be uniform enough to Warrant the 

 continuation of investigations along these lines. As they stand they indicate 

 that sex in Bufo may be determined at or near the time of fertilization, and 

 that external factors acting during this period may influence the sex-deter- 

 mining mechanism in such a way as to produce one sex or the other. The 

 results also indicate that sex is determined in the egg and that it may in 



