294 THE GYPSY MOTH. 



From the above experiments we conclude that a temper- 

 ature of at least 140° is necessary to destroy the vitality of 

 the developed embryo in the egg. In March, 1895, the 

 effect of the naphtha torch flame was tried upon egg-clus- 

 ters, exposing them to the action of the flame for various 

 short periods of time. This apparatus is sometimes used for 

 destroying eggs laid in cavities in trees. Of thirty-one egg- 

 clusters treated in this manner none hatched. 



JEJfect of Cold on Eggs, 

 Experiments in rapidly changing egg-clusters from a high 

 to a low temperature were conducted with the following re- 

 sults : March 22, 1895, four egg-clusters were changed in 

 twenty minutes from a temperature of 80° above zero to 5° 

 above, and left over night in a freezing mixture of calcium 

 chloride and snow. Two of the egg-clusters hatched April 9 

 and two April 11. Apparently these egg-clusters hatched 

 as well as the average ones in the field, and the caterpillars 

 from them fed and grew in as satisfactory a manner as 

 normal caterpillars. March 26, two egg-clusters were ex- 

 posed for some time to a temperature of 80° F. They were 

 then packed in a mixture of calcium chloride and snow, and 

 in fifteen minutes reduced to a temperature of 20" below 

 zero, a fall of 100°. They were kept at this temperature for 

 thirty minutes, and then taken out and placed in the hatch- 

 ing-box. By the 16th of April all had hatched. 



Date of Hatching. 



The eggs of the gypsy moth hatch in the spring, from the 

 last of April to the middle of June, depending on the weather 

 and the places in which they are deposited, those eggs which 

 are laid in warm, sunny places hatching the earliest, while 

 those that are laid in cold places, being protected from the 

 heat of the sun, hatch much later. The earliest recorded 

 date of hatching in the field was April 1, 1892, in Medford, 

 and on May 14 of the same year a large part of the eggs in 

 warm, sunny places had hatched. The latest date noted was 

 June 17. 



The embryo develops very rapidly, especially in a warm 

 temperature. Eggs laid Aug. 10, 1894, showed well-de- 



