INSECTA. 815 
butterflies, which would not naturally have been 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 ia 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 pupe 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 odtected 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 the 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 The members are also withdrawn from a 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 mining 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. Inthe 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 meni 
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 sta‘e 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, ca.- 
eulated for action in a lifferent situation or in a different melium. The 
elytra assume their brilliant colors; the wings expand to their p,oper size, 
and assume their various workings ; and what seemed a few minutes before 
