INSECT. 



83.5 



wanting ; whilst in others the terminal segments are 

 furnished with membranous (false or pro)-legs. In 

 other species, however (the number of which is but 

 comparatively small), the insect nearly resembles its 

 parents, being, however, destitute of wings. This vari- 

 ation naturally introduces two principal divisions 

 amongst insects, the former being said to have a 

 complete metamorphosis, and the kilter an incom- 

 plete one ; but as these terms have also been em- 

 ployed by Linnaeus and Fabricius in a more restricted 

 and totally different sense, and as they have been 

 applied to designate the entire metamorphosis, instead 

 of simply indicating the formation of the larva, we 

 prefer dividing insects, from a 'consideration of their 

 larvae, into two divisions, which may thence be named 

 Heteromorpha and Homomorpha. 



In all this diversity, however, there is still a general 

 prevailing uniformity of structure, which, under various 

 modifications of form, preserves a tendency towards 

 one typical organisation. This typicality in larvae 

 consists in having the body ordinarily composed of 

 thirteen segments, which are for the most part of 

 an equal size, although when arrived at maturity, 

 some of the&e segments become obsolete, being con- 

 rerted into internal organs, or are greatly altered as 

 regards the extent of their individual development. 

 Here the entire object of the animal's existence con- 

 sists in its capability of feeding ; consequently, owing 

 to the formation of the internal digestive organs, the 

 body maintains throughout its various segments a 

 general conformity, none requiring an extra develop- 

 ment for the support of organs fitted for other pur- 

 poses. When, however, the insect has arrived at the 

 perfect state, its objects are completely altered, it has 

 now to seek its mate; it. is therefore provided with 

 wings, which requiring support from the segments to 

 which they are attached, cause these segments to be 

 necessarily developed in an extraordinary degree ; 

 the other adjacent segments being losers : the insect 

 has also now to perform the great object of its ex- 

 istence, namely, the continuing of its kind, and there- 

 fore the organs of generation become organs of 

 especial importance, and we accordingly find other 

 portions of the body sacrificed for their development. 

 The thirteen segments which compose the body of 

 the larva bear the following relation to the distri- 

 bution of the segments in the imago. The first 

 segment or head of the larva becomes the head of the 

 imago; the three following segments compose the 

 thorax, and the remainder become the abdomen in 

 the perfect insect. Dr. Ratzeburg has, indeed, lately 

 published a memoir, endeavouring to prove that the 

 two first segments of the larva of the aculeate Hymen- 

 oplera become the head of the imago ; but the ob- 

 servations of this author, as we have proved more 

 than once, are incorrect, and founded upon very 

 unphilosophical views. 



In the Homomorphous division, the larvae greatly 

 resemble the perfect insect, differing chiefly in being 

 entirely destitute of any appearance of the organs of 

 flight. The second segment of the body also 

 does not exhibit the shield-like scutellum which is 

 found in the imago in that situation ; here belong the 

 various tribes of locusts, grasshoppers, and crickets 

 (fig. 11, larva of the cricket), bugs (fig. 12, larva of a 

 Pcntatoma), tree and frog-hoppers, cockroaches, prey- 

 ing mantes, &c., constituting the orders, Orthoptera, 

 Hemiptcra, and Homoptera, as well as some portions 

 the order Neuroptera. Some of these insects are, 



however, remarkable for being destitute of wrings in 

 the perfect state, and a difficulty thence arises of dis- 

 tinguishing the larvae from the subsequent states. 

 The variation in their size, and the constant absence 

 of ocelli, as well as a somewhat less perfectly de- 

 veloped organisation of the antennae; these, and 

 some other parts of their structure, may serve to 

 distinguish them. From analogy with the higher ani- 

 mals, we might, perhaps, be induced to consider that 

 these insects which maintain a constant activity 

 throughout their existence, are much higher in the 

 scale of nature than those species which, like the 

 butterfly, are subject to so long a period of death-like 

 repose. 



In the Heteromorphout division the larva is totally 

 unlike the perfect insect, being generally more or less 

 vermiform, and, with the exception of the head, of a 

 leathery-like texture. Here belong the tribes of 

 beetles, butterflies, moths, bees, and most other four 

 and two-winged flies, as well as the flea. There are, 

 however, various modifications of form in respect to 

 the head and egs of the larvae of those insects, so that 

 it may, perhaps, be advisable to give a sketch of their 

 distribution, proceeding from the more fully to the 

 less perfectly developed species. 



A. Larixs capitatcB, or those having a distinct head, 



sub-divisible into 



1. Hyperhefapodtz, or those having six legs, and 



a variable number of membranous prolegs. 

 The larva; of butterflies (fig. 14, larva of 

 Camberwell beauty butterfly), moths and 

 saw-flies (fig. 13, larva of Cimbex lutea). 



2. Hexapodae, or those having six scaly legs, but 



being destitute of prolegs. The larva? of 

 many Coleoptera (fig. 15, larva of Trichius 

 noblis), and some Neuroptera. 



3. Apodes, or those destitute of legs and prolegs. 



Many Coleoptera, Hymenoptera (fig. 16, 

 larva of wild bee), gnats and tipulse (fig. 18,' 

 larva of Tipula), and the flea (fig. 17, 

 larva). 



B. Larvce ecapitatte, or those without a distinct 



scaly head, including the majority of dipterous 

 insects (fig. 19, larva of the flesh fly), some 

 few of which are furnished with membranous 

 tubercles serving as prolegs. 



The head, in the generally of larvae, is covered 

 with a corneous case, often divided by an impressed 

 .ine running down the middle of the face, into two 

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