428 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 



52° to —4°, without injury or material hastening of the hatch.— [Riley's Experi- 

 ments, 3. 



Eggs, out of doors, at Saint Louis, from November 15 to March 2, and therefore 

 exposed to 80 days of maximum temperature lower than 51°, and 20 days of maximum 

 temperature over 58°. The eggs continued hatching from March 2 to April 10. — 

 [Riley's Experiments, 6. 



Eggs buried at Manhattan, Kans., November 10, at depths from 1 to 18 inches. 

 Examined May 12, and had all hatched down to 12 inches, but none below that. — 

 [Riley's Experiments, p. 356. 



Eggs hatched in from 7 to 14 days at temperature of 78°. It is not known whether, 

 in these experiments, the eggs were perfectly fresh, nor whether the temperature was 

 perfectly uniform. — [Smith and Trask. 



From these observations, and having in mind the irregularities in the 

 time of oviposition, and the possibility of the previous exposure of some 

 of these eggs to an unknown though small amount of natural heat 

 before being subjected to the artificial experimental temperature, the 

 following estimate or rather " working hypothesis " has been formed as 

 to the approximate relation between the temperature and the time of 

 hatching.^^ 



At a uniform temperature of 50° Fahrenheit, the eggs require 65 

 whole days or, 1,560 hours. 



At a uniform temperature of 60^ Fahrenheit, the eggs require 60 

 whole days, or 1,44:0 hours. 



At a uniform temperature of 70° Fahrenheit, the eggs require 55 

 whole days, or 1,320 hours. 



Whether eggs will hatch on exposure to a continuous temperature 

 much higher or lower than these may be questioned. Analogy shows 

 that there must be a limiting temperature. 



APPLICATION OF PRECEDING DATA TO THE ESTIMATION OF THE DATES 

 OF HATCHING OF EGOS DEPOSITED UNDER NATURAL CONDITIONS. 



In order to apply the estimates of the preceding section to the locust 

 eggs actually lying in the ground, we must, in the absence of direct ob- 

 servation of the soil temperature, find some general connection between 

 this and that of the air, as given by ordinary meteorological registers. 



This connection has been more elaborately treated of by numerous 

 authors ; but for our case the question is simplified by the fact that we 

 need only to have some general statement of the time during which soil 

 temperatures exceeding 50^ have prevailed For more accurate investi- 

 gation, and assuming that the thermal constants of the preceding sec- 

 tion can be determined with minute accuracy, we should imperatively 

 need observations of the actual temperature of soil rather than any ap- 

 proximate inferences. 



We propose for our present approximation to ascertain, first, on how 

 many days during the months in question air-maxima of 50^, 60^, &c., 



94 This estimate was made without knowledge of that given by Mr. Riley in Chapter VHI, where 

 the times are given as 28 to 35 days, at a temperature of 85° Fahrenheit, or 42 days, at a temperature of 

 75^ Fahrenheit, and at the moment of going to press there is not time to investigate the origin of this 

 difference. 



