344 STATES OF INSECTS. (Jmago.) 
brate animals. In these the duration of their life is in 
proportion to the term of their growth: those which at- 
tain to maturity the latest, in almost every case living the 
longest. In insects, on the contrary, we often meet with 
the very reverse of this rule. Thus the larva of the great 
goat-moth (Cossus ligniperda) is three years, that of the 
cabbage-butterfly (Pontia Brassice) not three months, in 
attaining maturity; yet the perfect insects live equally 
long. Melolontha vulgaris, which in its first state lives 
four years, as a beetle lives only eight or ten days?*. 
And some Ephemera, whose larvee have been two years 
in acquiring their full size, live only an hour; while the 
flesh-fly, whose larva has attained to maturity in three or 
four days, will exist several weeks. 
There is yet another anomaly in the duration of the 
life of perfect insects. This is not, asin larger animals, 
a fixed period liable to be shortened only by accident or 
disease, and incapable of being prolonged ; but an inde-~ 
terminate one, whose duration is dependent on the ear- 
lier or later fulfilment of a particular animal function— 
that ofpropagation. The general law is, that a few days, 
or at most weeks, after the union of the sexes, both pe- 
rish, the female having first deposited her eggs. If, 
therefore, this union takes place immediately after the 
disclosure of the insect from the pupa, their existence in 
the perfect state will not exceed a few days or weeks, or 
in some cases hours, as in that of the Ephemera, and like- 
wise of the Phalene Attaci, L. &c., which fall down dead 
immediately after oviposition”. But if by any means it 
be put off or prevented, their life may be protracted to 
three or four times that period. Gleditsch asserts, that 
* Dumeril Traité Elément. ii. 87. n. 683, » De Geer ii, 288. 
