EXTERNAL ANATOMY OF INSECTS. 575 
pear to enter the chest, the use of which I shall explain 
hereafter. In the Libellulina, as I shall soon have oc- 
casion to show, there is a peculiar arrangement of the legs 
and wings, in consequence of which this part is placed 
behind the posterior ones. In the remaining Orders, the 
mesostethium, though it exists, exhibits no peculiarities 
worthy of particular notice, except in some Apfera and 
Arachnida: thus, in the bird-louse of the goose (Nirmus 
Anseris) it is terminated posteriorly by apair of transverse 
membranous appendages which cover the base of the 
posterior core ; in Scorpio it consists of two pieces, the 
pectines* being attached to the sides of the posterior 
one. 
15. Parapleura®. The parapleura, speaking gene- 
rally, is that piece of the postpectus which, intervening 
between the pleura, mesostethium, and scapulars, is at- 
tached by its posterior extremity to the core of the hind- 
legs; by means of the pleura, from which it does not 
appear to be separated by any suture, it connects the 
secondary or under-wings with the hind-legs, as the sca- 
pular does the primary ones with the mid-legs; so that 
the direction of the parapleura depends upon the rela- 
tive situation of the legs and wings. In Coleopterous 
insects its direction is horizontal, it being generally a nar- 
row subquadrangular piece that runs straight from the 
posterior coxz to the scapular °, and usually divided into 
two unequal portions by an elevated or impressed line. 
In the palm-weevil (Cordylia Palmarum) this part is 
wider than usual; in Dytiscus marginalis,—in which ge- 
nus, as likewise in Carabus, &c. the core are incapable of 
2 Prate XXVIHI. Fic. 50. 6 Prates VIII. IX. 2’. 
° Prate VIM. Fic. 4. 2’. 
