EFFECTS OF HEAT ON TOAD'S EGG. 2IQ 



temperature and their later development compared with that of 

 the eggs in the control set. 



II. EXPERIMENTS ON UNSEGMENTED EGGS. 



Experiment i . On April 1 6, twenty-five unsegmented eggs 

 were subjected to a temperature of 28-30 C. for two and one- 

 half hours. When removed from the chamber, all of the eggs 

 were in the id-cell stage, while in the control set, developing at 

 room temperature, the eggs had only reached the 4-8 -cell stage. 

 The immediate effect of the higher temperature, therefore, was 

 to increase the rate of development. This result agrees fully 

 with that obtained by Hertwig in many of his temperature ex- 

 periments on the frog's egg. The later development of the 

 eggs in this series appeared to be perfectly normal, and it took 

 place at about the same rate as in the eggs of the control set. 



Experiment 2.-- A number of eggs that had not yet seg- 

 mented were put into water at a temperature of 30-32 C. on 

 April 17. Part of the eggs were removed at the expiration of 

 three quarters of an hour, and when examined they were all 

 found to be segmenting. In a few cases the first cleavage plane 

 had nearly cut through the yolk portion of the egg and the 

 second furrow was appearing. In the control set of eggs, the 

 first cleavage plane was just coming in at this time, so that, in this 

 experiment also, the early development became more rapid as an 

 immediate result of exposing the eggs to a higher temperature. 

 All of these eggs developed into normal embryos. 



Some of the eggs of the above lot remained in the heated 

 chamber for one hour. The second cleavage plane had ap- 

 peared in all of the eggs when they were removed to room tem- 

 perature. Later segmentation was normal, and on the following 

 day the dorsal lip of the blastopore appeared in all of the eggs 

 at about the same time that it formed in the eggs of the control 

 set. On April 1 9, many of the eggs were dead ; some were in 

 the early gastrula stages, and some showed traces of the medul- 

 lary folds. Of the seven embryos alive on April 20, three were 

 abnormal, having a large yolk plug exposed at the posterior end 

 of the body ; the other four embryos were normal and were kept 

 for several weeks. 



