LABRUM. 249 



fluid, the necessity for biting jaws is obviated. They are 

 therefore either obsolete, or they assume the form of lancets, 

 and as such have a motion quite diiFerent from that of the 

 jaws of biting insects. The mouth of these insects exhibits 

 two distinct modifications of form. In the first, the four 

 lateral pieces, or the mandibles and maxillae, are converted 

 into slender, setiform, or lancet-like pieces, forming a kind 

 of sucker, which is received into a membranous conical or 

 cylindrical and articulated gutter, as in the bugs ; or are 

 lodged within a thick, elbowed, and fleshy sheath, as in the 

 flies. In the second modification, the upper lip and the man- 

 dibles are either obsolete or but very minute ; the lower lip 

 IS no longer a distinct and loose organ, but is attached to the 

 head, and is distinguished only by a pair of large palpi ; the 

 maxillas, on the contrary, are greatly elongated, but very 

 much attenuated, being transformed into two tubular threads, 

 which, uniting at the edges, form a kind of sucker, generally 

 rolled up in a spiral direction, and furnished at the base with 

 two minute palpi. I v,i\\ now take the organs of the mouth 

 seriatim, according to their position, commencing with that 

 which lies uppermost, or. 



The Labrum, or upper lip (Z 1 in the figures). — This organ 

 is, in biting insects, a horny or leathery flattened plate of 

 variable form, attached, by an articulation, to the clypeus. 



B^ ^ jk^ 



9i ^^ 93 ,9^. 



Figs. 91, Labrum of IMegacephala — 92, ditto of Aploa— 93, Perilampus— 94, lianclms. 



and serving as an upper covering to the rest of the mouth : 

 unlike the lower lip, this organ is never furnished with palpi. 



