INSECT. 



845 



specimen of Bombyx menthastri, and six of Opkiun 

 v'uiula, hatched from the pupts of Bombyx vlmdiis, 

 which is certainly a curious fact" We presume from 

 this statement, which is, however, sufficiently desti- 

 tute of precision, that these various specimens were 

 produced from a single pupa of the puss moth. On 

 throwing oft' the pupa covering, the arrival at the per- 

 fect state is ordinarily completed ; hut a remarkable 

 exception to this occurs in the Ephemera;, of which 

 we have given an account in our article upon these 

 insects. We will, therefore, only add that this occur- 

 rence of a subsequent moulting in this group does not 

 seem to warrant the conclusion, that the preceding 

 state is not that of the pupa, nor to overthrow the 

 opinion that the pupa state ought not to be regarded 

 as a distinct one. We apprehend, indeed, that as 

 the Lepidnptera and the dragon flies are known to shed 

 '.. similar pellicle, its existence throughout the winged 

 insects ought, from analogy, to be presumed, until di- 

 rect observation proves the contrary. 

 We are now to examine 



Section III. The general structure of insects as es- 

 pecialh/ exhibited in their perfect state. Our atten- 

 tion must no\v be directed to the final and perfect 

 state of insects, and in the first place to their struc- 

 tural peculiarities. This branch of the subject will 

 naturally divide itself into two branches, first, the 

 anatomy ot the external parts of the body ; and 

 secondly, that of the internal organs. 



1. External anatomy. Insects being animals des- 

 titute of any interior skeleton, it is necessary that 

 their external covering should be much thickened, 

 and rendered sufficiently strong to giv support to the 

 numerous muscles which are internally attached to it. 

 Hence in the majority of insects this covering is of a 

 scaly or horny consistence. It is, however, modified 

 by the nature of the habits of the individual. Thus 

 the Aphides, Hemerobius, Ephemera, and other short- 

 lived insects, have the skin very soft ; whilst those 

 which generally take up their abode beneath stones, 

 under the bark of trees, in water, &c., are more 

 strongly defended against accidents by the solidity ol 

 their envelope, than those which live upon flowers. 

 Those, also, which reside beneath the bark of trees 

 or under stones, have a flattened form, whilst those 

 which burrow into wood are cylindrical. 



The body of insects consists of a series of rings 

 connected and articulating with each other, by the 

 assistance of muscular membranes, whereby the insect 

 is enabled to contract or lengthen, narrow or dilate, its 

 body, and so give to it all the necessary movements 

 We have said that the external integuments of in- 

 sects exhibited a horny appearance, nevertheless there 

 is no real analogy between the scaly covering of a 

 beetle, and horn, their chemical properties being quite 

 distinct ; to be convinced of which, it is sufficient to 

 apply them separately to the flame of a lamp ; anc 

 the same distinction is proved by placing them in a 

 solution of potash, of the temperature of boiling 

 water, in which the horn will be dissolved ; but the 

 covering of the beetle undergoes no change, except tha 

 of loss of colour. The base of the latter is found, b 

 chemical analysis, to consist of a peculiar substance 

 found only in the integument of annulose animals 

 which has been termed chitine, and which forms th 

 outer covering ; albumen also, an animal extract, t 

 small portion of carbonate of potash, phosphate o 

 lime, and phosphate of iron, and an oil variable in 

 colour according to the colours of the organs froir 



which it is extracted, form parts of the insect integu- 

 ment, but chitine is by far the greatest portion of the 

 materials of which it is composed. 



By Linnteus, the body of an insect was divided 

 nto four parts, the head, trunk, abdomen, and limb?. 

 The latter, however, more properly belong to the 

 econd of these divisions, of which they are appen- 

 ages ; and the term thorax is now generally applied 

 o designate the Linnaean trunk. Hence we have now 

 o treat upon the head, thorax, and abdomen. These 

 hree divisions, as respectively comprising the princi- 

 )al organs of sensation, locomotion and generation, 

 ippear to be completely in unison with nature, and 

 mve accordingly been universally adopted and em- 

 ployed. That persons ignorant of the comparative 

 anatomy of insects should have blundered in their 

 rivial descriptions of insects, and miscalled any of 

 hese parts, can be no argument against their correct- 

 ness ; neither can we at all comprehend the assertions 

 of a recent author, who would impose, in lieu of this 

 distribution, a useless (as it appears to us) series of 

 names for each individual segment, stating that " their 

 wings are either thoracical or abdominal appendages, 

 as an entomologist pleases,"* and that, therefore, 

 there are no such parts in an insect as a thorax or an 

 abdomen. 



But in addition to these three primary divisions, the 

 jody of insects consists of a series of secondary divi- 

 sions, or rings, of which the head exhibits no distinct 

 trace ; the thorax, on the contrary, is always divisible 

 into three segments ; and the abdomen is, in general, 

 variable in the numbers of its segments from six to 

 nine, exclusive of the organs of generation. On com- 

 paring the different segments of a perfect insect, 

 various striking differences will be observed, depend- 

 ing principally upon the presence or absence of the 

 appendages, or organs, which these segments respec- 

 tively support, as well as upon the degree of their de- 

 velopment. Thus when one of these segments has 

 attained its greatest extent and complication, and the 

 appendages, which it supports, have reached theii 

 maximum, it is presumed that the segment itself is 

 composed of a certain number of distinct pieces, more 

 or less distinct, with which it is essential to possess an 

 acquaintance. To arrive at this result, it is evident 

 that we must examine one of the thoracic segments in 



* Newman on the Osteology, or External Anatomy of Insects, 

 a series of letters commenced in the Entomological Magazine, 

 and containing a great deal of very valuable matter, but written 

 in a style quite perplexing to a learner whilst endeavouring: to 

 unravel many of the statements which it contains. Thus, when 

 the author asserts that the limits of the abdomen have been al- 

 ways ideal; that the abdomen may comprise either seven, eight, 

 nine, ten, or eleven of the thirteen segments of an insect's 

 body ; and that, consequently, the wings of a beetle are gene- 

 rally considered abdominal ; a tyro relying implicitly upon 

 such a statement, would conclude that the researches of all pre- 

 vious anatomists had been of the most unphilosophical kind. 

 Mr. Newman must, however, be well aware that there is not the 

 least shadow of a foundation for them to rest upon. Linnaeus 

 and his followers, it is true, restricted the name of thorax in the 

 beetles, to the first segment following the head, but did it thenre 

 follow that all the remaining segments must necessarily be ab- 

 dominal? This would, indeed, be the case, if Linnajus had divi- 

 ded the body of an insect into the head, thorui, and abdomen ; 

 but this is not the fact. He says, "corpus dividitur in caput, 

 truncuui, abdomen, artus ;" and he subsequently gives the 

 thorax as a compound part of the truncus, which he says is si- 

 tuated "inter caput et abdomen." Thus, by speaking of the 

 term thorax, when used in its Linn a;an. restricted sense, as 

 though it had "~>een used in its now most general sense for the 

 whole Linnseantrur.cus, the learner is left in doubt ; and all prece- 

 ding authors made to appear absolute fools, and yet the authoi 

 himself is enabled, by the researches of these very men, *o gain 

 credit for having introduced a most philosophic simplicity into 

 the science of insect anatomy, with the majority of his readers. 



