566 



INSECTS AND AEACHNIDA. 



some of these parts are mucli more highly developed in other 

 insects, other parts may be so much altered or so little developed, 

 as to he scarcely recognizable. The Coleoptera present the 

 typical conformation of the mandibulate mouth, which is adapted 

 for the prehension and division of solid substances; and this 

 consists of the following parts : — 1. A pair of jaws, termed 

 mandibles, frequently furnished with powerful teeth, opening 

 laterally on either side of the mouth, and serving as the chief 

 instruments of manducation ; 2. A second pair of jaws, termed 

 maxillce, smaller and weaker than the preceding, beneath which 

 they are placed, and serving to hold the food, and to convey it to 

 the back part of the mouth ; 3, an upper lip, or labrum ; 4, a 

 lower lip, or labium; 5, one or two pairs of small jointed appen- 

 dages termed palpi, attached to the maxillse, and hence called 

 maxillary palpi ; 6, a pair of labial palpi. The labium is often 

 composed of several distinct parts ; its basal portion being dis- 

 tinguished as the mentum or chin, and its anterior portion being 

 sometimes considerably prolonged forwards, so as to form an 

 organ which is properly designated the ligula, but which is more 

 commonly known as the "tongue," though not really entitled to 



Fia. 287. 



Tongue of common Fly :—a. lobes of lijula; b, poriion enclosing the lancets formed by the 

 metamorphosis of the maxilla; c, maxillary palpi :— a, portion of one of the metamorphosed tracheie 

 enlarged. 



that designation, the real tongue being a soft and projecting 

 organ that forms the floor of the mouth, and being only found 

 as a distinct part in a comparatively small number of insects, as 



