INSECT. 



657 



This is the segment which immediately follows the ' 

 head, and precedes the segment bearing the anterior I 

 pair of wings. On its under side it bears the anterior 

 pair of legs. It is generally larger than the head, 

 and smaller or narrower than the following segment ; 

 the reason whereof is obvious, since it has only to 

 support one pair of limbs, whereas the following sup- 

 ports two. It is to the upper surface of this piece, 

 when most fully developed, that Linnaeus gave the 

 name of thorax. It is named by Kirby prothorax, 

 by Audouin tergum, and by Burmeister pronotum. 

 But the four dorsal pieces are here confluent*, 

 although, as in some locusts, their situation is indi- 

 cated by transverse impressions across the prothoracic 

 shield. 



The size of the pronotum (T) varies very consider- 

 ably as well as its form ; thus whilst in the Coleoptera, 

 Orthoptera, and heteropterous Hemiptera, it is of a 

 vcrv large size and forms a strong horny shield (see 

 ri-s. 11(3, 118, T 1), sometimes produced over the 

 whole body, and in others furnished with the most 

 remarkable protuberances, as in many Homoptera, 

 lamellicorn beetles, &c. In the Lc.idoptera and 

 Tiicli(>i>tcrn it is nearly evanescent, forming in the 

 first of these orders a narrow ring. In some Hymen- 

 optera. it is more conspicuous, forming, as in Xyphi- 

 dria, a narrosv neck, by which the head is attached to 

 the thorax. In this order, the front of the thorax is 

 covered by a narrow plate (see figs. 124, 125, c 1), 

 which often laterally reaches as far as the base of the 

 wings. This is the collare of Kirby, who contends 

 that it ought not to be regarded as a part of the pro- 

 thorax. MacLeay, Burmeister, and others, however, 

 give it as a portion of that segment, the former con- 

 sidering it as the scutellum of the prothorax, and ob- 

 serving that as these insects are essentially fliers, this 

 piece of the prothorax is employed to add strength 

 to the mesothurax in its support of the upper wings. 

 The under surface of the prothorax (T 1) consists 

 of a central piece or prosternum (antepectus, K.), 

 which is generally horny, and extends in a point 

 between the tore-legs, as is especially the case in the 

 spring beetles (Elaterida), and two lateral pieces 

 which are very distinct in the predaceous beetles. 

 These are the epimera and episterna of Audouin, 

 and sometimes the ora of Kirby and Spence. 



In addition to the various horns or protuberances 

 which arise from the prothorax, but which are only 

 continuations of the external crust, there are several 

 distinct appendages to be noticed. Of these, the legs 

 are the most important, the basal piece of which often 

 appears to form a constituent part of the prosternum, 

 but is, nevertheless, moveable ; the first pair of spira- 

 cles are also parts of the prothorax. 



Moreover, in some of the longicorn beetles there is 

 a pair of moveable spines (umbones, Kirby and 

 Spence), arising at the sides of the pronotum ; and 

 in lepidopterous insects there is a pair of scales 

 covered with hair, quite distinct from the wing-rovers 

 (teguIaeX and which the same authors term patagia, 



or tippets; but which have been overlooked by all 

 other authors except Chabrier, who first discovered 



Ti 



* Hence MacLeay say.s that in all future descriptions the 

 four confluent dorsal pieces of the prothorax (which are almost 

 invariably, at least in the Colenptem, &c.,) described as the 

 thorax by the ('.lumbers of species should no longrer be called 

 the thorax but the prothorax ; but this must surely not be cor- 



Figs. 124, dorsal view of the thorax of a wasp; 125, lateral vievr 

 of ditto, lettered as in fijrs. 118123. 



them, or else confounded (as by Burmeister, p. 77), 

 with the true tegulae. They are descrioed as vesicles 

 appearing full of liquid and of air, and are placed at 

 the sides of the pronotum. 



2. The Mesothorax. (Prolhorajr, Strauss-Diirck- 

 heim) T2 and(T)2. 



This is the second segment of the thorax (or the 

 first of the alitrunk of Kirby and Spence), and bears 

 the anterior pair of wings, or their representatives, 

 and the middle pair of legs. In insects which have the 

 four wings of equal size, the mesothorax and the 

 metathorax, (the following segment), are equally de- 

 veloped ; but when, on the contrary, one pair of these 

 organs is more particularly developed, the segment to 

 which it is attached is consequently increased in size.. 

 If this pair of wings be the anterior pair, the mesotho- 

 rax is greatly enlarged, this is, therefore, the case in the 

 Dipiera (fig! 126), where the mesothorax almost occu- 

 pies the entire thorax. In the Hymenoptera (fig. 124) 

 the second pair of wings exist, but of a smaller size 

 than the fore pair ; the metathorax is accordingly more 

 developed than in the Diptera, but is smaller than 

 the mesothorax. If we now look at those orders 

 which have the second pair of wings enlarged, we 

 find the mesothorax diminished, and the metathorax 

 increased in size to a corresponding extent ; this is 

 the case in the beetles, but most especially in the 

 extraordinary parasitic order, Strepriplera, respecting 

 which so much incorrect matter has been published. 

 The four pieces of which the upper side of each 

 thoracic segment is typically composed, are suffici- 

 ently distinct in the niesonotum; the first, or the prse- 

 scutum (a 2), (prophragma, Kirby and Spence) ; and 



LULJJ 



-Tl 



the thorax but the prothorax ; but this must surely not be cor- /2/ 126 



rect, since the latter name would imply both upper and lower , iat-rnl 



surface of the first thoracic sceim-nt, although the descriptions Figs. 126, dorsal view of the thorax or a Tab**} 12,, lateiat 



are applicable only to the ter-um or upper surface of this seg- view ot ditto, lettered us in figs. 1 18-12.5. 



ment. Burmeister has obviated the difficulty by proposing the 

 term pronotum. 



the second, b '2, scutum (or the dorsulum, Kirby and 



