INSECTA. 335 



the semi-annulus to which they belong, the extent and direction of 

 that semi-annulus varying, furnish the thorax, thus considered, with 

 a combination 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 undertaken at my request, by the late 

 Lachat. His friend, M. Victor Audouin, has prosecuted his re- 

 searches and presented to the Academie des Sciences an excellent 

 memoir on the subject. All that is yet known of it, however, is 

 from the general sketch given by the Baron Cuvier in his report *, 



* The exposition of the parts of the thorax, and a fixed nomenclature created 

 for them, says the Baron in his report, should naturally be placed at the head of 

 the work. The trunk of Insects is always divisible into three annuli, each of which 

 bears a pair of legs, called by M. Audouin, from their position, the prothorax, the 

 mesothorax, and the metathorax. Besides these legs, the mesothorax bears the first 

 pair of wings, and the metathorax the second. Each of these three segments is 

 composed of four parts: one inferior, two lateral (forming the pectus), and a 

 fourth superior, which constitutes the back : the inferior is called the sternum ; the 

 lateral portion, or the flank, is divided into three principal parts, one which is 

 attached to the sternum, called ejnsternum, another behind the first, and to which 

 the coxa is articulated, the epimera (epimere). A little moveable piece, hitherto 

 unknown, which serves to unite the epimera and the coxa, is named trochantinus, 

 (trochantin) by way of distinguishing it from trochanter. The third piece of the 

 flank, which in the mesothorax and metathorax is situated before the episternum 

 and under the wing, is called the hypothera. Sometimes there is also a small cor- 

 neous piece round the stigma, styled the perifrema. The superior portion of each 

 segment, which the author calls tergum, is divided into four pieces, named, from 

 their position in each ring, prascutum, scutum, and posfscutellum. The first is fre- 

 quently, and the fourth almost always, concealed in the interior. Naturalists have 

 seldom distinguished any other part of the mesothorax but the scutellum, which is 

 frequently remarkable for its large size and its configuration, although an analogous 

 piece is found in the three segments. Thus the tnink of Insects may be divided 

 into thirty-three principal parts, and, if we count the hypothera, the number will 

 amount to forty-three, more or less visible in the interior. From these pieces, 

 besides, arise various internal productions, which, on account of their uses and im- 

 portance, require to be named : thus, from the posterior portion of the sternum of 

 each segment, a vertical apophysis arises internally, sometimes shaped like a Y, 

 called by M. Audouin the entothorax. It furnishes insertions to muscles and pro- 

 tects the medullary cord ; an analogous one is seen in the head and sometimes in 

 the first annuli of the abdomen. Other internal prominences result from the pro- 

 longation of the external neighbouring pieces that are soldered together. M. Au- 

 douin names them apudema (apodemes). Some of them give insertion to muscles, 

 others to the wings : — finally, there are other small moveable pieces either internally 

 and between the muscles, or at the base of the wings, which our author styles the 

 (^pidemes) epidema. We have stated that the principal pieces, or vestiges of them, 

 are always to be found, but they are frequently far from being separable. In par- 

 ticular genera, or in certain orders, many are only to be distinguished by traces of 

 sutures. M. Audouin — Diet. Class. d'Hist. Nat., art. Iiisectes — has since substi- 

 tuted the name of parapttra for that of hypoptera. That of entothorax will also be 

 changed, in some situations, into entocephahi, relative to the head — and into ento- 

 gaster, as respects the abdomen. He remarks that the head of Insects is composed 

 of several segments. We have also observed, that the rostrum of the Cicadee, repre- 

 senting the lower lip, is not attached to the head but to the membrane which 



