THE EFFECTS OF HEAT ON THE DEVELOPMENT 



OF THE TOAD'S EGG. 



HELEN DEAN KING. 



An extended series of experiments made by Hertwig (1-4) 

 prove that the maximum temperature at which the eggs of the 

 frog will develop normally differs for different species. His ex- 

 periments also show that eggs in the cleavage stages can with- 

 stand a higher temperature than can unsegmented eggs. These 

 results have a bearing on the general problem of adaptation ; for 

 it may be possible to show, after more species have been studied, 

 that the maximum temperature which the eggs of amphibians 

 can endure without injury and also the temperature most* favor- 

 able for their development depend, to a certain extent at least, on 

 the time of year at which the eggs are deposited. 



MATERIAL AND METHOD. 



The eggs of the common toad, Biifo lentiginosus, were used 

 in making all of the experiments recorded in the present paper. 

 After natural fertilization, the eggs were brought into the labora- 

 tory where the temperature varied from 18 to 2 1 C. Control sets 

 of eggs from each lot used for the experiments, developing at 

 the room temperature, all became perfectly normal embryos, and 

 some of them were kept until metamorphosis. 



In making the experiments, small dishes containing about 80 

 c.c. of spring water were placed in the drying chamber of a large 

 water-bath, and after the water had become heated, from 50 to 75 

 eggs were quickly transferred into it and left a given length of 

 time. The temperature to which the eggs were being subjected 

 could readily be told from a thermometer that projected into 

 the chamber through a small opening in the top. Great care 

 was taken to keep the temperature of the chamber as constant 

 as possible during the course of the experiments, and in no case 

 did it vary more than two degrees. After the eggs were re- 

 moved from the chamber, they were put into fresh water at room 



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