INSECT A. 231 



its application within proper limits, we will employ that term 

 in all those eases where this segment is much larger than the 

 others, and where these latter are joined to the abdomen, and 

 seem to constitute an integral part of it a disposition proper 

 to the Coleoptera, Orthoptera, and several of the Hemiptera. 

 When the prothorax is short, and forms with the succeeding 

 segments a common and exposed mass, the trunk composed of 

 the three will retain the name of thorax. We will also con- 

 tinue to style pectus the inferior surface of the trunk, dividing 

 it according to the segments, into three areas, the ante-pectus, 

 medio pectus, and post-pectus. The median line will also con- 

 stitute 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 annul us itself, which 

 bears a stigma, so that the sides of the abdomen present a lon- 

 gitudinal series of small pieces, or each segment seems to be 

 quadripartite. Other equally corneous pieces occupy the in- 

 ferior sides of the mesothorax and metathorax and immediately 

 under the origin of the elytra and wings, which are supported 

 by another longitudinal 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 the semi-annulus to which 

 they belong, the extent and direction of that semi-annulus 

 varying, furnish the thorax, thus considered, with a combi- 

 nation of characters, which in a systematic point of view are 

 of great importance. Some naturalists, Knoch in particular, 

 had already employed them, but on no fixed principle, and 

 under arbitrary denominations. A necessary preliminary step 

 was the careful and comparative study of the thorax, as it 

 exists in all the orders of the class of Insects. This was 



