INSECTA. 343 



two parts; the one, inferior and solid, is the mentum or chin; the 

 other, which is usually provided with two palpi, is the ligula. 



In the Suctoria, or those that live by the suction of fluid aliment, 

 these various organs of manducation present themselves under two 

 kinds of general modifications. In the first, the mandibles and the 

 jaws are replaced by little lamina? in the form of seta? or lancets, 

 forming, by their union, a sort of sucker, which is received into a 

 sheath, supplying the place of a labium, and is either cylindrical or 

 conical, and articulated in the form of a rostrum, or fleshy or mem- 

 branous, inarticulated, and terminated by two lips constituting a 

 proboscis. The labrum is triangular and arched, and covers the 

 base of the sucker. 



In the second modification, the labrum and mandibles are nearly 

 obliterated, or are extremely small: the labium is no longer free, 

 and is only distinguishable by the presence of two palpi, to which 

 it gives insertion: the jaws have acquired a most extraordinary 

 length, and are transformed into tubular filaments, which, being 

 united at their edges, compose a sort of spiral proboscis called the 

 tongue, but which, to avoid all equivocation, it would be better to 

 call spirignatha; its interior exhibits three canals, the intermediate 

 of which is the duct of the alimentary juices. At the base of each 

 of these filaments is a palpus, usually very small, and but slightly 

 apparent. 



The Myriapoda are the only insects in which the mouth presents 

 another mode of organization it will be explained in treating of 

 that order. 



The trunk of insects, or that intermediate portion of their body 

 which bears the legs, is generally designated by the term thorax, or 

 corselet by the French. It is composed of three segments, not well 

 distinguished at first, the relative proportions of which vary consi- 

 derably. Sometimes, as in the Coleoptera, the anterior, much the 

 largest, separated from the following one by an articulation, mova- 

 ble, and alone exposed, appears at the first glance to constitute the 

 entire trunk, and is called the thorax or corselet; sometimes, as in 

 the Hymenoptera, Lepidoptera, &c., it is much shorter than the 

 ensuing one, has the appearance of a collar, and, with the two 

 others, forms a common body, attached to the abdomen by a pedi- 

 cle, or adhering closely to it across its whole posterior width, and 

 is also called thorax. These distinctions were insufficient, and M. 



