Jj44 external anatomy of insects. 



substance, while the prosternum is hard, resembling a 

 bone. In other instances these parts are both of the 

 same substance. 



1. The sternum or breast-bone of insects consists 

 mostly of three distinct pieces ; in this resembling the 

 human sternum, which is described by anatomists as 

 composed originally of three bones a . 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 Cetoniadce 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 b : 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 Coleoptera Or- 

 der, to which my remarks upon it will be chiefly con- 

 fined. In these it is sometimes an elevation, and some- 

 times 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 per- 

 ceive between the head and the arms a triangular vertical 

 process, with a longitudinal cavity on its posterior face, 

 which receives the point of the mesosternum that passes 

 between the arms c : this vertical piece is the real pro- 

 sternum, 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 



a Monro On the Bones, 160. b Plate VIII. d'. 



c Ibid. Fig. 7. d'. 



