INSECT A. 229 



In tlie Suctoria^ or those that live by the suction of fluid 

 aliment, these various organs of manducation present them- 

 selves under two kinds of general modifications. In the first, 

 the mandibles and the jaws are replaced by little laminse in 

 the form of setae 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 membranous, 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 fila- 

 ments, 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 inte- 

 rior 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 appa- 

 rent. 



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(l) of insects, or that intermediate portion of 

 their body which bears the legs, is generally designated by 



(1) This teriTij here, is synonymous with that of thorax. In order to avoid con- 

 fusion, I think it would be better to restrict the application of the former to the 

 Linnaean Aptera with more than six legs, and where those organs are borne by par- 

 ticular segmen'ts, that is, where the head is distinct from the trunk. With respect 

 to the Crustacea in which these parts of the body are confounded, the thorax 

 might be called thoracida; and cephalo-tliorax in the Arachnides, animals present- 

 ing the same character, but in which the trunk or thorax is more simple and pro- 

 vided with fewer appendages. The Entomostraca, in this respect, approach the 

 latter, but as they belong to another class, the term thorucida should still be ap- 

 plied to them; that of thorax would then be exclusively appropriated to the Ilexa- 

 poda. 



