INSECTS. 237 



or later fulfilment of a particular function. The general law 

 regarding this period among insects seems to be, that a few 

 days, or at most a few weeks, after the union of the sexes and 

 the deposition of the ova by the female, both individuals perish. 

 The period for effecting this is longer or shorter, according to 

 the species. Some, as several Ephemera, live only a few hours, 

 and never enjoy the enlivening light of the sun, appearing only 

 to fulfil the great purpose of nature after sunset, and having 

 finished this in the course of a few hours, by dropping their ova 

 on the surface of their native waters, perish before the dawn- 

 ing of another day. Others, as flies, moths, butterflies, and 

 indeed the greater part of insects, take a few days or weeks to 

 accomplish the same purpose. A comparatively small number, 

 such as some of the larger Coleoptera, Orthoptera, &c. exist from 

 six to nine, twelve, and even fifteen months ; and some instan- 

 ces have been recorded of particular species, when kept and fed, 

 having their existence prolonged considerably beyond this term. 

 But these are exceptions to the general rule. And it is to be 

 remarked further, that insect life seems to follow a different 

 law from that which prevails among vertebrated animals, where 

 the duration of existence is generally observed to be in relation 

 to the period of their attaining maturity, that is, that an ani- 

 mal is long or short lived in proportion as it attains puberty 

 in a longer or shorter period. Among insects this analogy does 

 not hold ; for while the larvae of the goat-moth (Cossus ligni- 

 perda) is three years, and that of the cabbage butterfly not 

 three months in attaining maturity, yet the perfect insect 

 in both lives equally long. The Mdolontha vulgaris, which 

 exists four years in its preparatory stages, lives only eight or ten 

 days as a perfect insect ; some Ephemeras, whose larvge have 

 enjoyed two years of preparatory existence, scarcely live beyond 

 an hour ; while the common flesh-fly, whose larvae have attain- 

 ed to maturity in three or four days, exists several weeks. It 

 is worthy of remark, as connected with this subject, that al- 

 though the general rule seems to be that insects die immediate- 

 ly or soon after the period when the continuance of the species 

 is provided for by their coupling and the deposition of the ova, 

 yet, if the junction of the sexes be prevented, such individuals 

 seem exempted from the general law. It is probable that some 

 of the instances related of insects having been kept for long pe- 



