566 EXTERNAL ANATOMY OF INSECTS. 



triangular transverse anterior piece, which in fact seems 

 only marked by a black channel, to which also interiorly 

 a ridge is opposed a . In the rest of the Order it is divided 

 longitudinally into two parallel pieces. In Panorpa the 

 posterior piece is longer than the anterior and props 

 the coxa behind ; in Myrmeleon and Perla, &c, it ap- 

 pears to consist of three pieces. I have not been able to 

 obtain a clear idea of them in the Lepidoptera, except 

 that they have more than one piece. Hymenopterous 

 and Dipterous insects for the most part have no scapular 

 distinct from the peristethium ; but in Cimbex, Perga, 

 and other saw-flies, it seems represented by its posterior 

 depressed and sometimes membranous part : in Vespa, 

 &c. a small subtriangular piece, just below the base of 

 the upper wing, is probably its analogue 5 . 



8. Mesosternum c . The central part of the medipectus, 

 or that which passes between the mid-legs when ele- 

 vated, protended, or otherwise remarkable, is called the 

 mesosternum or mid-breast-bone. In the Coleoptera Or- 

 der it exhibits the most numerous variations, and is 

 usually the most strongly marked of any of the three 

 portions of the sternum, affording often important cha- 

 racters for the discrimination of genera and subgenera. 

 It may be said to be formed upon three principal types — 

 the first is, where it is a process of the posterior part of 

 the peristethium, and points towards the anus or the 

 head ; — the second, where it is a process of the anterior 

 part of the mesostethium, and points only towards the 

 head: in this case there is no suture to separate the 



3 Plate IX. Fig. 8. a. b Ibid. Fig. 12. o. 



c Plate VIII. Fig. 3, 13. p'. 



