GENERATIONS OR BROODS OF INSECTS. 



21 



"We have observed that certain species of insects and often individ- 

 ual insects may without any assignable reason remain a considerably 

 longer time than usual in the pupa state. Lyda stellata usually has a 

 single brood (one year generation) while it frequently happens that 

 from the pupa beginning the first of May, the imago does not fly at the 

 end of May or in June, as is the rule, but that the pupa state lasts over 

 to the next May, when the adult flies. The pupal rest in this case lasts, 

 instead of three weeks, more than a year. A similar case is that of 

 CnetJiocampa pinivora. This relation is connected with the fact that 

 insects are cold-blooded, or better, poikilothermic, i. e., changeably warm 

 animals. We understand thereby such animals as those whose peculiar 

 body heat, although constantly a little higher than that of the surround- 

 ing medium, the air, water or earth, i. e., their habitat, yet varies with 

 the changing temperature of this medium. In contrast with these are 

 the warm-blooded, or, more exactly, the homoeothennal, i. e., animals with 

 an even temperature which as long as they live steadily maintain their 

 own normal temperature up to a height ranging at most 1° C. Tbe 

 blood-heat of a healthy man, although he may be exposed to a degree 

 of cold of — 30O C. or a warmth of + 30° C,, remains steadily at 38° O. 

 (Judeich and Nitsche.)* 



The duration of development of a warm-blooded animal is definite. 

 The development of an insect's eggs, however, is analogous to that of 

 a fish. We best see this when at the beginning of spring the leafing 

 out of the foliage is late and the caterpillars of Clisiocampa hatch cor- 

 respondingly late. Exact series of observations of indubitable cer- 

 tainty are scarcely at hand, but, add our authors,! we will cite the posi- 

 tive statements of Eegeuer| on the influence of temperature on the 

 duration of development and of life of the pine Bombyx at different 

 temperatures, though, indeed, they are somewhat inexact and incom- 

 plete. 



Provisional tabular view of the life-history of the Pine spinner {Gaslropacha pini) at dif- 

 ferent temperatures, after Regener. 



* Each degree of the Centigrade thermometer is equal to ip of Fahrenheit; and 

 0^ is at the freezing point of water. 



tJudeich and Nitsche, I, 116. 



X E. Regener. Erfahrungen iiber den Nahrungsverbrauch nud iiber die Lebens- 

 weise, Lebensdauer nnd Vertilgung der grossen Kiefernraupe. Leipzig : Emil 

 Baeusch's Verlag. 1865. 



