254 



INSECTA. 



merable modifications adapting them to different offices. The 

 mouths of all creatures are constructed upon purely mechanical 

 principles ; and in few classes of the animal world have we more 

 beautiful illustrations of design and contrivance than in that before 

 us : -jaws armed with strong and penetrating hooks for seizing 

 and securing active and struggling prey, sharp and powerful 

 shears for clipping and dividing the softer parts of vegetables, 

 saws, files, and augers for excavating and boring the harder parts 

 of plants, lancets for piercing the skin of living animals, 

 siphons and sucking tubes for imbibing fluid nutriment ; all 

 these, in a thousand forms, are met with in the insect world, 

 and thus provide them with the means of obtaining food adapted 

 to their habits, and even of constructing for themselves edifices 

 of inimitable workmanship. 



(295.) Parts of the mouth. The mouths of insects may be di- 

 vided into two great classes, those which are adapted for biting, 

 forming what is called a perfect or mandibulate mouth ; and those 

 which are so constructed as only to be employed in sucking, consti- 

 tuting the suctorial or haustellate mouth. It is in the former of these 

 divisions that all the parts composing the oral apparatus are most 

 completely developed . we shall therefore commence by describ- 

 ing the different pieces of which a perfect mouth consists, viz. 

 an upper and an under lip, and four horny jaws. We select the 

 dragon-fly (fig 112, A) as an example. The upper lip (labrum, 



Fig, 112. 



B) is a somewhat convex corneous plate, placed transversely across 

 the upper margin of the cavity wherein the jaws are lodged, so that, 

 when the mouth is shut, it folds down to meet the under lip (la- 



