TAWS OF INSECTS. 93 



forin tolerably accurate ideas of the kind of food on which 

 the insect naturally subsists.* 



Above, or rather in front of the mandibles, is situated the 

 labrum, or upper lip (u.) It is usually of a hard or horny 

 texture, and admits of some degree of motion: but its form 

 and direction are exceedingly various in different tribes of 

 insects. The lower pair of jaws (j,) or maxillx, as they 

 have been termed, are behind the mandibles, and between 

 them is situated the labium, or lower lip (l,) which closes 

 the mouth below, as the lahrum does above. In the grass- 

 hopper, each maxilla consists of an outer and an inner plate 

 (o and I.) The jaws of insects are confined, by their arti- 

 culations with the head, to motions in a horizontal plane 

 only, so that they open and close by a lateral movement, and 

 not vertically upwards and downwards, as is the case with 

 the jaws of vertebrated animals. The maxillcC are, in most 

 cases, employed principally for holding the substances on 

 which the dividing or grinding apparatus of the mandibles 

 is exerted. A similar use may be assigned also to the or- 

 gans denominated Palpi, or Aiitennulx (p, q,) which are 

 jointed filaments, or processes, attached to different parts of 

 the mouth, and most usually to the maxillae and the labium; 

 the former (p) being termed the maxillay^y , and the latter 

 (q) the labial palpi. In addition to these parts, another, 

 which, from its supposed use, has been denominated Glossa^ 

 or tongue (g,) is also generally found. 



For an account of the various modifications which these 

 parts receive in different tribes and species, I must refer to 

 works which treat professedly of this branch of comparative 

 anatomy. I shall content myself with giving a single exam- 

 ple of the conversion of structure here alluded to, in that of 

 the I'ostrum, or proboscis of the Cimex nigricoriiis. This 

 insect belongs l(\ the order Hemiptera, which has been 

 usually characterized as being destitute of both mandibles 



* See a memoir by Marcel tics Scrrcs, in the Annalcs du MusC'um d'llist. 

 Nat. xiv. 56. 



