IN SECT A. 815 



butterflies, which would not naturally have teen developed till the following 

 May, in a hot-house, and the result was, that the perfect insects made their 

 appearance in a fortnight, in the depth of winter ; and by other experiments 

 he ascertained that in this high temperature the change was accomplished in 

 five or six days, which would have required as many weeks in ordinary 

 circumstances. The converse of this experiment equally succeeded ; for by 

 keeping pupae in an ice-house during the whole summer, the production of 

 the fly was retarded a full year beyond the ordinary period. And it is a fact 

 well ascertained that the pupa state sometimes continues for years — thus 

 providing for the continuance of the species, should adverse seasons threaten 

 to destroy the inclosed animals before they had carried through the great 

 purpose of nature by reproduction. The mode in which insects break 

 through their prison-house or coccoon, and assume the perfect form, is' vari- 

 ous. Previous to this period, the color of the pupa undergoes an alteration : 

 the golden or silver tinge in many vanishes, and those which are transpa- 

 rent usually permit the form and colors of the insect within and the motions 

 of their limbs to be seen. In the obtccted pupa, the struggles of the included 

 butterfly or moth first effect a longitudinal slit down the middle of the thorax, 

 where there is usually a suture for ihe purpose, and the insect gradually 

 withdraws itself from its case. The members are also withdrawn from a 

 a series of inner membranous sheaths, which separately include them like a 

 glove. In the coarctate pupa, where the outer case is generally more rigid 

 and destitute of sutures, a lid or operculum is found at the anterior end which 

 the animal is enabled to push off; and the coleopterous insects, whose tem- 

 porary dwelling is under ground, await the progress of the developement, 

 and hardening of their elytra, before raining upwards to the open air. In 

 other families, the coccoon is ruptured by the inclosed insect ; or in cases 

 where the portions of the cases have been glued together, that glue is dis- 

 solved by a solvent fluid, and the animal left free to escape ; and among the 

 ants, the working class not only feed the young previously, but at their 

 period of transformation cut the minute threads of the coccoons when the 

 insect is ready to appear. In the gnat, which undergoes its change on the 

 surface of the water, the pupa-case splits like a little boat, and the animal 

 raises itself from the horizontal to the vertical position, extricates its mem- 

 bers from their confinement, rests for a moment on the water till its wings 

 are unfolded, and flies away. 



The last stage of the life of insects is termed the imago or perfect state. 

 In this state all their parts are fully developed, and it is only in this stage 

 that they are qualified for the great purpose of reproduction. Immediately 

 upon their exclusion, insects are generally weak, soft, and languid ; and 

 some short space of time is required for the expansion of the members, cal- 

 culated for action in a different situation or in a different medium. The 

 elytra assume their brilliant colors ; the wings expand to their proper size, 

 and assume their various workings ; and what seemed a few minutes before 



