302 NATURAL HISTORY OF ARTHROPODS. 



them with flies and other insects, care being taken that the full-grown larvae have 

 opportunity to crawl out of the water and into moist sand, in which latter they pupate. 

 Carnivorous land-coleoptera are more difficult to rear. Where a large number of the 

 same species of beetle is reared at once, specimens of each stage should be preserved 

 in alcohol, carefully labelled, for future reference. 



In bodily form the Coleoptera present every variation from long cylindrical to 

 nearly globular, from hemispheres to extremely flattened discs, from straggling ant- 

 like forms to compact seed-like ones, as may be seen by examining the illustrations 

 which follow. Throughout all the diversity of form which environment has given 

 beetles, they invariably show, with considerable distinctness, a division into three 

 parts, portions which, at first sight, might easily be mistaken for head, thorax, and 

 abdomen, but which more careful examination proves to be head, prothorax, or the 

 first of the three divisions of the thorax, and a portion, covered generally by the elj'- 

 tra, which is composed of the mesothorax or middle portion of the thorax, the meta- 

 thorax or posterior part of the thorax, and finally the abdomen. The head bears for 

 appendages the antennae and mouth-parts ; the prothorax, the first pair of legs ; the 

 mesothorax, the elytra and middle pair of legs ; the metathorax, the wings and hind 

 pair of legs ; the abdomen, only the genitalia, which are usually concealed in beetles. 

 The prothorax moves with considerable freedom on the mesothorax, and this articula- 

 tion is a character of importance in the separation of the Coleoptera from the 

 Hymenoptera, Diptera, and other insects, in which the three divisions of the thorax are 

 more or less firmly united together.^ These divisions, head, prothorax, mesothorax, 

 metathorax, and abdomen, with their appendages, merit much further consideration. 



The head of Coleoptera, both in their larval and adult states, bears the mouth-jjarts 

 directly forward and slightly downward as in many Carabidfe, or directly downward 

 toward the surface on which the insect is standing, as in many Chrysomelidse. Later- 

 ally the head of the adult beetle bears compound eyes, usually large, and the antennae 

 are generally just in front of the eyes. "With few exceptions, among which may be 

 mentioned certain Dermestidae, ocelli are absent in the images of Coleoptera; the com- 

 pound eyes are absent or functionless only in a very few cave-inhabiting species. In 

 the larvae, where compound eyes fail, there are often ocelli — from one to seven, 

 usually six, on each side. 



The antennffi, which are not only organs of touch, but much moi-e olfactory organs, 

 present considerable diversity in form in adult beetles. Often these organs are better 

 developed on the male than on the female, becoming marked secondary sexual char- 

 acters ; this is especially the case with the lamelliform antennae of some of the species 

 of Scarabaeidfe. In certain families the antennae are not very conspicuous, and can be 

 hidden in grooves, as in the Elateridse ; in other families, as in the Cerambycidfe, the 

 antennae are prominent organs, often, in the last mentioned family, exceeding the 

 length of the insect, in some species double or treble its length. In a few families, as 

 in the Scolytidse, which have very small antennae, important generic characters are 

 found in these organs. The antennae of beetles may have from two to thirty-four 

 joints, but eleven is the usual number. The antennse of most beetle larvae have but 

 four joints ; rarely they have five, three, or two joints, and in certain cases they are 

 represented only by a very small inarticulate tubercle. 



Beetles have, without exception, biting or chewing mouth-parts. More or less 

 concealed beneath a well-developed labrum, itself articulated to the epistoma or cly- 

 peus, is a pair of chitinous mandibles. In the males of Lucanus the mandibles attain 



