EXTERNAL ANATOMY OF INSECTS. 577 



times rhomboidal, and other forms of it occur. Between 

 the hind-legs it. generally terminates in a notch or bifur- 

 cation distinct from the metasternum, as in Hydrophilus, 

 &c. ; in Hister there is no notch, and in many Scara- 

 bmdcE it projects between the hind-legs in a truncated 

 or rounded mucro; in the Vesicatory beetles, Meloe 

 L., it is more elevated than the medipectus, towards 

 which it descends almost vertically ; in Dytiscus L., Ca- 

 rabus L., &c, this part is usually divided into two by a 

 transverse sinuous channel, and in Elater by a longitu- 

 dinal straight one. In many Orthopterous genera, Gryl- 

 lotalpa, Acrida K., Locusta Leach, &c, the mesostethium 

 consists of two pieces a . It is remarkable that in many of 

 these genera, in this part, as likewise in the medipectus and 

 antepectus, are one or more perforations which appear to 

 enter the chest, the use of which I shall explain hereafter. 

 In the Libellulina, as I shall soon have occasion to shew, 

 there is a peculiar arrangement of the legs and wings, in 

 consequence of which this partis placed behind the pos- 

 terior ones. In the remaining Orders, the mesostethium, 

 though it exists, exhibits no peculiarities worthy of par- 

 ticular notice, except in some Aptera and Arachnida: 

 thus, in Nirmus Anseris it is terminated posteriorly by 

 a pair of transverse membranous appendages which 

 cover the base of the posterior coxae ; in Scorpio it con- 

 sists of two pieces, the pectines h being attached to the 

 sides of the posterior one. 



15. Parapleural. The parapleura, speaking gene- 

 rally, is that piece of the postpectus which, intervening 

 between the pleura, mesostethium, and scapulars, is at- 



a Plate VIIT. Fig. 13. y. a f. b Plate XXVII. Fig. 50. 



c Plates VIII. IX. z'. 

 VOL. III. 2 1* 



