230 INSKCTA. 



the term thorax, or corselet by the JFrencli. It is composed 

 of three segments, not well distinguished at first, the relative 

 proportions of which vary considerably. Sometimes, as in the 

 Coleoptera, the anterior, much the largest, separated from the 

 following one by an articulation, movable, and alone exposed, 

 appears at the first glance to constitute the entire trunk, and is 

 called the thorax or corselet; sometimes, as in the Hymenopte- 

 ra, Lepidoptcra, &c., it is much shorter than the ensuing one, 

 has the appearance of a collar, and, with the two others, forms 

 a common body, attached to the abdomen by a pedicle, or 

 adhering closely to it across its whole posterior width, and 

 is also called thorax. These distinctions were insufficient, 

 and frequently ambiguous, inasmuch as they were not based 

 on a ternary division, distinctly announced by me in the first 

 edition of this work, as a character proper to the Hexapoda. 

 M. Kirby having already employed the denomination of mc- 

 tathoi-ax, to designate the after- thorax(l), that of prothorax 

 and mesothorax, the ternary division once established, natu- 

 rally presented itself to the mind, and the celebrated professor 

 Nit2sch was the first to employ it. Some naturalists have 

 since designated the prothorax or anterior segment, that 

 which bears the two first feet, by the term collar, collare. 

 Wishing to retain the denomination of corselet^ but to restrain 



(1) This segment should not be restricted, in the Hymenoptera, to tliis superior, 

 very short, and transverse division of the thorax, on the sides of which the second 

 wing's are inserted. It is also formed of that portion of the thorax which extends 

 backwards to the origin of the abdomen, a circumstance which evidently demon- 

 strates the position of the two last stigmata of the trunk, they being placed on the 

 sides of this extremit)-^, behind the wings, and above the last pair of legs. I am 

 even of the opinion that this observation will apply to all winged Insects. Their 

 metathorax should be divided, at least above, into two parts or semi-segments, one, 

 in the Tetraptera, bearing the second wings and destitute of stigmata, and the 

 other furnished with them; sometimes this latter portion, as in nearly all Insects, 

 the Hymenoptera with a pediculated abdomen, the Rhipiptcra and Diptera ex- 

 cepted, appears to belong to the abdomen; sometimes it is incorj)orated with the 

 trunk or thorax and closes it posteriorly, as in those last mentioned. In the Or- 

 thoptera, Hymenoptera, Lepidoptera and Diptera, the two anterior or thoracic 

 segments are placed between the prothorax and the mesothorax. The abdomen 

 will then consist of nine complete segments, the three last of which compose the 

 organs of generation. 



