542 EXTERNAL ANATOMY OF INSECTS. 
leathery substance, while the prosternum is hard, resem-— 
bling a bone. In other instances these parts are both of 
the same substance. 
1. The sternum or breast-bone of insects consists 
mostly of ¢hree distinct pieces; in this resembling the 
human sternum, which is described by anatomists as 
composed originally of three bones*. Each of these 
pieces is appropriated to a pair of legs, and each of them 
at times has been called the sternum : thus in Elater the 
prosternum, in the Cetoniade the mesosternum, and in Hy- 
drophilus the metasternum, have been distinguished by 
this name. Our business is now with the first of these 
pieces, the sternum of the antepectus or prosternum : this 
is the middle longitudinal ridge of the fore-breast, which 
passes between the arms, when elevated, extended, or 
otherwise remarkable. It is most important in the Cole- 
optera Order, to which my remarks upon it will be 
chiefly confined. In these it is sometimes an elevation, 
and sometimes a horizontal process of the fore-breast. If 
you examine the great Hydrophilus (H. piceus), at first 
you will think that there is only a single sternum common 
to all the legs; but if you look more closely, you will 
perceive between the head and the arms a triangular ver- 
tical process, with a longitudinal cavity on its posterior 
face, which receives the point of the mesosternum that 
passes between the arms“: this vertical piece is the real 
prosternum, and not the other, which really belongs to 
the alitrunk. In this case the elevation of the prosternum 
is before the arms; in others it is between them, as you 
may see ina Chinese chafer (Mimela), which imitates 
* Monro On the Bones, 160. > Prate VIII. d’. 
© Ibid. Fic. 7. d’. 
