THE MOUTH. VJ 



ant characters for the classification of the innumerable 

 beings belonging to this class. Thus in some cases 

 the mouth is adapted for biting solid substances, the 

 different organs of which it is composed being modi- 

 fied in their form according to the nature of the bodies 

 upon which they are to be exercised ; in others, the 

 nutriment is taken entirely in a fluid form, and the 

 mouth is arranged accordingly, so as to furnish an 

 apparatus for suction, at the same time that, when 

 necessary, some parts of it are adapted to the pro- 

 duction of wounds in the tissues of plants and animals 

 upon whose fluids the creatures feed; but notwith- 

 standing this diversity of function, it is remarkable 

 that in all these animals the fundamental structure of 

 the mouth is essentially the same, and the investiga- 

 tions of comparative anatomists have proved, that, 

 however dissimilar they may appear, the organs form- 

 ing the mouth are identical in all insects. 



In the mouth of an ordinary biting insect these 

 organs are as follows. The aperture of the mouth is 

 bounded in front by a small horny plate, which is 

 moveably articulated to the lower part of the front of 

 the head (called the clypeus) . This is the labrum or 

 upper lip ; it varies greatly in size and form, and its 

 peculiarities often furnish characters of importance for 

 the distinction of different groups. Immediately 

 below this is a pair of horny jaws, each composed of a 

 single piece, and articulated by a sort of hinge-joint, 

 one on each side of the opening of the mouth. Thesa 

 are called the mandibles-, they are usually strong, 

 curved and pointed, and very commonly armed with 

 teeth on their inner edge, or at the tip. The man- 

 dibles form the principal agents in biting, and it is by 

 the aid of these that many insects are enabled to gnaw 



B 5 



