EXPERIMENTS ON EGGS. 293 



To obtain extremes of cold, the eggs were placed in vials 

 and enclosed in a small can, which was then placed in an- 

 other can containing a freezing mixture (composed of equal 

 parts of coarse granulated snow and salt, and in some cases 

 one which was composed of four parts of snow and five parts 

 of calcium chloride). The degree of cold was indicated by 

 a thermometer placed in the freezing mixture, and so ar- 

 ranged as to be easily read through a glass window in the 

 side of the can. 



Effect of Heat on Eggs. 



On April 3, ten egg-clusters of the gypsy moth were ex- 

 posed for thirty minutes to a temperature of 80 F. They 

 were then placed in the hatching-boxes, where the temper- 

 ature was normal, and daily observations made until April 

 16, when all the egg-clusters were found to have hatched. 

 April 3, ten egg-clusters were exposed for thirty minutes 

 to a temperature of 90, and were then placed in hatching- 

 boxes ; all of the clusters had hatched April 16. April 

 3, ten egg-clusters were exposed for thirty minutes to a 

 temperature of 100, and then placed in hatching-boxes ; by 

 April 17, all had hatched. April 3, ten egg-clusters were 

 exposed for thirty minutes to a temperature of 110, and 

 then placed in hatching-boxes ; on the 17th of April all of 

 these egg-clusters had hatched. March 26, three egg-clusters 

 were exposed for thirty minutes to a temperature of 120, 

 and then placed in hatching-boxes ; one of these hatched 

 April 7 and the other two on April 9. On April 3, ten egg- 

 clusters were exposed for thirty minutes to a temperature of 

 130, and then placed in hatching-boxes; on April 12, all 

 of these egg-clusters commenced hatching. Having obtained 

 this result, they were further experimented with by being 

 placed in a cold box surrounded by ice and salt, and ex- 

 posed for thirty minutes to a temperature ranging from zero 

 to 8 below; none of the egg-clusters hatched after this 

 treatment. April 15, ten egg-clusters were exposed for a 

 period of fifteen minutes to a temperature of 140; none 

 hatched. April 16, six egg-clusters were exposed to a tem- 

 perature of 150 for a period of fifteen minutes, and then 

 placed in the hatching-boxes ; none hatched. 



