States of insects. 345 



goat-moth (Cossus ligniperdcty is three years, that of the 

 cabbage-butterfly (Pieris Brassicce) 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 a . 

 And some Ephemera, whose larvae 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, as in 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 of propagation. 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 Phalcena Attaci L. &c, which fall down dead 

 immediately after oviposition b . 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 

 by keeping apart the sexes of a grasshopper, their lives 

 were prolonged to eight or nine weeks, instead of two or 

 three, their ordinary length; and under similar circum- 

 stances Ephemera, which usually perish in a day, have 



a Dumeril Traile Element, ii. 87- n. 683. b Be Geer ii. '2§8. 



