STRUCTURE OF LARVJE. 163 



' it is,' to follow the excellent description of Kirby 

 and Spence, ' by far the largest organ of the mouth, 

 which, when closed, it entirely conceals, and it not 

 only retains but actually seizes the animal's prey, by 

 means of a very singular pair of jaws with which it is 

 furnished. Conceive your under-lip (to have recourse, 

 like R aumur on another occasion, to such a compa- 

 rison) to be horny instead of fleshy, and to be elon- 

 gated perpendicularly d!)wnwards, so as to wrap over 

 your chin, and extend to its bottom, — that this elon- 

 gation is there expanded into a triangular convex plate, 

 attached to it by a joint, so as to bend upwards 

 again and fold over the face as high as the nose, con- 

 ceahng not only the chin and the first-mentioned 

 elongation, but the mouth and part of the cheeks: 

 conceive, moreover, that to the end of this last-men- 

 tioned plate are fixed two other convex ones, so broad 

 as to cover the whole nose and temples, — that these 

 can open at pleasure transversely like a pair of jaws, 

 so as to expose the nose and mouth, and that their 

 inner edges where they meet are cut into numerous 

 sharp teeth, or spines, or armed with one or more long 

 sharp claws; — you will then have as accurate an 

 idea as my powers of description can give of the 

 strange conformation of the under-lip in the larvas of 

 Libellulina, which conceals the mouth and face pre- 

 cisely as I have supposed a similar construction of 

 your lip would do yours. You will, probably, admit 

 that your own visage would present an appearance 

 not very engaging while concealed by such a mask; 

 but it would strike still more awe into the spectators, 

 were they to see you first open the two upper jaw 

 plates, which would project from each temple like the 

 blinders of a horse; and next, having, by means of 

 the joint at your chin, let down the whole apparatus 

 and uncovered your face, employ them in seizing any 



