228 HELEN DEAN KING. 



Experiment 18. Eggs in early gastrulation stages were ex- 

 posed to a temperature of 37-38 C. on April 24. A part of 

 the eggs were removed at the end of one quarter of an hour. 

 None of these eggs seemed to be injured in any way by the high 

 degree of heat to which they had been subjected and all de- 

 veloped, somewhat slowly, into normal embryos. The rest of 

 the eggs in this lot remained at the temperature of 37-38 C. for 

 one hour. They were all dead when removed to room tem- 

 perature. 



The results of the experiments in this series show that eggs in 

 the 32-64-cell stage cannot withstand a temperature of 31-33 

 C. for a much longer period than can eggs that have just begun 

 to segment. The maximum temperature to which eggs can be 

 subjected without injury is practically the same for unsegmented 

 eggs and for those in early cleavage stages, although eggs in the 

 later stages can remain at this temperature for a somewhat longer 

 period and still develop normally. 



Eggs in late cleavage stages have a much greater power to 

 withstand high temperature than have eggs in the earlier stages 

 of development, as they will develop normally after exposure to 

 a temperature of 3637 C. for one-half of an hour. The maxi- 

 mum degree of heat that can be endured without injury is still 

 higher for eggs in the gastrula stages, as they become normal 

 embryos after being subjected to a temperature of 37-38 C. for 

 one quarter of an hour. 



The experiments described above are summarized in the fol- 

 lowing table. The number of the experiment is given in the 

 first column ; the condition of the eggs when the experiment was 

 begun in the second column ; the temperature to which the eggs 

 were subjected in the third column ; followed in the next two 

 columns by the duration of the experiment and a brief statement 

 of the results. 



The results of these experiments are very similar to those ob- 

 tained by Hertwig (14) in his study of the effects of heat on the 

 development of the eggs of various species of frogs ; and the 

 abnormalities produced resemble, in many respects, those which 

 Hertwig has described and figured. When the unsegmented 

 eggs of Bufo lentiginosus are subjected to a temperature that 



