PATITS OF INSECTS, 3l 



the Hrimenapkra and Lepldopteru a large plane of one or more joints in- 

 tervenes between the true thorax and the sciitcl ; and it is to this last- 

 inentioned dorsal space that the term thorax is assigned. Hence it is 

 evident that the language of Entomology in this point is not altogether 

 consistent; because what we denominate the collar in Hi/menoptera, 

 is the thorax in Cukoptcm ; and in Culeuptera we tind nothing analo- 

 gous to the tliorax of the other order, except the collar. 



The thorax in those insects which have that part consisting of a 

 single piece, or the hrst segment in such as are of a compound nature, 

 has the first pair of legs arising from the lower surface, and it is in 

 this part that the muscles which move the head as well as this pair of 

 less are said to be contained. The thorax in difierent kinds of insects 

 varies considerably in form, and aftbrds very excellent generic and spe- 

 citic distinctions. Some are armed with spines, others denticulated, 

 marginated, &c. 



Pectus, the Breast, is the third segment of the body, or that to which 

 the tour posterior feet are attached, and which is longitudinally di- 

 vided at the anterior part of the sternum. The wings in lepidopterous 

 and most other insects have their origin or l^ase in tlie superior part 

 of the breast. The wings and elytra in the Coleoptera and Hemiptera 

 deviate a little from this, as they are placed more immediately on the 

 back than in a lateral position; the breast contains the muscles that 

 move the wings and give action to the four posterior legs. This part 

 is capa])le of l)eing compressed and dilated, the alternate motion of 

 which is very evident in some insects of the butterfly or moth kind 

 when held between the fingers. The power of compression and dila- 

 tation is supposed to arise from the action of some very strong mus- 

 cles, being reddish yellow, and extremely loose. It has been con- 

 jectiu-ed that these muscles may assist the motions of the organs of 

 liight. 



Sternum, or Breast-bone. By this term entomologists define tliat por- 

 tion of the middle part of the breast which is situated between the 

 base of the four posterior legs. This piece terminates in some insects 

 anteriorly in a somewhat acute point; in others it appears rather bi- 

 lobate ; and in the far greater number ends obtusely or in an obtuse 

 lobe. There are few insects in which the stcrnwnis remarkable, eitlier 

 from its magnitude or figure. In some of the coleopterous tribes, as 

 in the Hydrophiti and Di/tici, this part is most conspicuous. 



ScuTELLUM (Linnc),the Scutel or Escutcheon: the lobe-like process si- 

 tuated immediately at the posterior part of the thorax in the scutellatc 

 insects. The scutel is not of the same form in all insects, yet its general 

 tendency is towards a sub-triangular figure. In the coleopterous tribes 

 it approaches nearest to this form; its deviations incline more or less to 

 heart-shaped, with the tip pointing backwards. The same figure pre- 

 vails in 5omc of the Ilcmiptcra. In the Ncuroptcra, liymcnoptcraf and 



