Glass 3. Insecta. 263 



Order 4. Coleoptera (Beetles.) 



The Coleoptera are holometabolous and have biting mouth-parts ; 

 the fore wings are modified to form elytra. The exoskeleton is usually 

 very firm, often brightly coloured. The head, which is partially sunk 

 into a depression of the prothorax, bears a pair of compound eyes of 

 diverse form; sometimes they are reniform, and the inpushing on 

 the front edge is in some cases so deep that each is divided into an 

 upper and a lower portion, and thus there are two compound eyes on 

 each side. Ocelli are almost always absent. The antennae usually 

 consist of eleven joints, but the number may be increased to about 

 thirty, or reduced to four ; in different species their form varies 

 considerably. The mandibles differ according to the food ; they are 

 slender in predaceous forms, thicker in herbivorous ; the mentum is 

 usually a well-developed, firmly-chitinised plate, whilst the rest of the 

 lower lip, with the exception of the palp, is usually only feebly 

 developed. The prothorax is large, strongly-chitinised, and freely 

 articulated with the mesothorax; between the prothorax and meso- 

 thorax there is a deep constriction. The mesothorax and metathorax, 

 ■of which the latter is best developed, are immovably connected; they 

 are covered above by the elytra so as to leave a scutellum ; the most 

 anterior portion of the mesothorax is covered by the hinder edge of 

 the prothorax. The tarsus is usually five-jointed, but there are not a 

 few exceptions to this. The fore wings are elytra, and during 

 rest they meet along the mid-dorsal line or may even be folded the 

 one over the other, whilst their lateral edges wrap round the lateral 

 edges of the body (Fig. 197) ; they thus form a very complete covering 

 not only for the hind wings but also for the dorsal surface of the 

 mesothorax and metathorax, and usually for most of the abdomen; 

 they are generally very hard. More rarely they are short, so that 

 the larger portion of the abdomen remains uncovered; in some 

 they overlap along the mid-line. The posterior are true wings, thin 

 and membranous, with few veins ; when at rest they are usually 

 folded not only lengthways but also transversely. In not a few 

 they are rudimentary or they may be absent, but in spite 

 ■of this, the elytra are generally just as well developed, since 

 they afford a covering for the abdomen ; both pairs of vrings are 

 wanting in only a very few cases. The abdominal somites are 

 divided into tergal and sternal half-rings, which are frequently 

 somewhat displaced; there are always fewer sterna (four to seven) 

 than terga (usually eight) ; the latter are less strongly chitinised 

 as far as they are covered by the elytra, the dorsal surface of the 

 abdomen is thus softer than the ventral. The larvse vary con- 

 siderably in form; they usually possess legs but may be maggot-like. 

 Only a few of the most important families of this extraordinarily large 

 order are mentioned here. 



