334 1NSECTA. 



prothorax and mesothorax, the ternary division once established, 

 naturally presented itself to the mind, and the celebrated professor 

 Nitzsch was the first to employ it. Some naturalists have since desig- 

 nated the prothorax or anterior segment, that which bears the two 

 first feet, by the term collar, collars. Wishing to retain the deno- 

 mination of corselet, but to restrain its application within proper 

 limits, we will employ that term in all those cases where this seg- 

 ment is much larger than the others, and where these latter are join- 

 ed to the abdomen, and seem to constitute an integral part of it a dis- 

 position proper to the Coleoptera, Orthoptera, and several of the 

 Hemiptera. When the prothorax is short, and forms with the suc- 

 ceeding segments a common and exposed mass, the trunk composed 

 of the three will retain the name of thorax. We will also continue 

 to style pectus the inferior surface of the trunk, dividing it according 

 to the segments, into three areae, the ante-pectus, medio-pectus, and 

 post-pectus. The median line will also constitute the sternum, which 

 we divide into three parts : the ante-sternum, medio-sternum, and 

 post-sternum. 



The teguments of the thoracic segments, as well as of those of the 

 abdomen, are usually divided into two annuli or semi-annuli, the one 

 dorsal or superior, the other inferior, laterally united by a soft and 

 flexible membrane, which, however, is but a portion of the same 

 tegument that in many Insects, the Coleoptera particularly, is less firm. 

 At the point of junction between these annuli we observe a little 

 space of a more solid texture, or of the consistence of the annulus 

 itself, which bears a stigma, so that the sides of the abdomen present 

 a longitudinal series of small pieces, or each segment seems to be 

 quadripartite. Other equally corneous pieces occupy the inferior 

 sides of the mesothorax and metathorax and immediately under the 

 origin of the elytra and wings, which are supported by another longi- 

 tudinal piece. The relations of these parts, the size and form of the 

 first joint of the coxae, the manner in which they are articulated with 



wings 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 demonstrates 

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

 this extremity, 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 fur- 

 nished with them ; sometimes this latter portion, as in nearly all Insects, the Hyme- 

 uoptera with a pediculated abdomen, the Rhipiptera and Diptera excepted, appears 

 to belong to abdomen sometimes it is incorporated with the trunk or thorax and closes 

 it posteriorly, as in those last mentioned. In the Orthoptera, Hymenoptera, Lepi- 

 doptera and Diptera, the two anterior or thoracic segments are placed between the 

 prothorax and the mesothorax. The abdomen will then consist of nine complete seg- 

 ments, the three last of which compose the organs of generation. 



