THORAX : PROTHORAX. 267 



1. The Prothorax (Manitrunk, Kirby), T 1, upper, and 

 (T) 1, under surface. This is the segment which imme- 

 diately follows the head, and precedes the segment bearing 

 the anterior 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 supports two. It is to 

 the upper surface of this piece, when most fully developed, 

 that Linnaeus gave the name of thorax, Kirby that of pro- 

 thorax, Audouin that of tergum, and Burmeister that of 

 pronotum; but the four dorsal pieces are here confluent*, 

 although, as in some locusts, their situation is indicated by 

 transverse impressions across the prothoracic shield. 



The size of the pronotum (T 1) varies very considerably as 

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

 and heteropterous Hemiptera, it is of a very large size, and 

 forms a strong horny shield (see figs. 116, 118, T 1), (some- 

 times produced over the whole body, and in others furnished 

 with the most remarkable protuberances, as in many 

 Homoptera, lamellicorn beetles, &c.), in the Lepidoptera and 

 Trichoptera it is nearly evanescent, forming in the first of 

 these orders a narrow ring. In some Hymenoptera it is more 

 conspicuous, forming, as in Xyphidria, a narrow 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 



* Hence MacLeay says, that in all future descriptions the four con- 

 fluent dorsal pieces of the prothorax, which are almost invariably (at least 

 in the Coleoptera, &c.) described as the thorax by the describers of species, 

 should no longer be called the thorax, but the prothorax ; but this must 

 surely not be correct, since the latter name would imply both upper and 

 lower surface of the first thoracic segment, although the descriptions are 

 applicable only to the tergum or upper surface of this segment. Bur- 

 meister has obviated the difficulty by proposing the term pronotum. 



