474 



Div. 3. ARTICULATED ANIMALS. 



cular trachea : this, however, as well as the choroid, is wanting in various darkling 

 insects ; 3rd, of nerves, which arise from a large trunk proceeding immediately from 

 the brain, which there dilates in a reversed conical form, the broad base being towards 

 the cornea, and of which the threads, running through the choroid and inner plaster of 

 the cornea, terminate separately in each of the facets. There is no crystalline nor 

 vitreous tumour. 



Many insects have, in addition to these composite eyes, simple eyes [oce///], the 

 cornea of which is smooth. They are generally three in number, and arranged in 

 a triangle upon the crown of the head. In the majority of apterous insects, and 

 the larvse of those which gain wings, the ocelli replace the eyes, and are often in- 

 serted in a group : judging from the eyes of the Arachnida, they are evidently fitted 

 for vision. 



The mouth of Hexapod insects is in general composed of six principal pieces, their 

 form being lateral, arranged in pairs, and mostly transversely ; and two others, opposed 

 to each other in a direction contrary to that of the preceding, filling up the space be- 

 tween the former : one is situated above the upper pair, and the other below the lower 

 pair. In the masticating insects, or those which feed upon solid materials, the four 

 lateral pieces perform the office of jaws (mdchoires) , and the two others are considered 

 as lips ; but, as we have already observed, the two upper jaws have been distinguished 

 by the particular name of mandibles, whilst the two others have alone retained the 

 name of maxillae (mdchoires) : the latter are also provided with one or two articulated 

 filaments which are called palpi, — a character which is never possessed, in this class, by 

 the mandibles. The extremity of the maxillae is often terminated by two divisions, or 

 lobes, of whicli the outer, in the Orthoptera, is termed the galea. We have already 

 said that the upper lip is called the lahrum. The other lip, or the labium {levre, pro- 

 perly so called), is formed of two parts: the one, solid and inferior, is the mentum; 

 the upper, which often bears two palpi, is the tonguelet (languette), [or Ugula'].* 



In the suctorial insects, or those which derive their food from fluid aliments, these 

 different organs of manducation appear under two general modifications. In the 

 first, the mandibles and maxillae are replaced by small, setaceous, lancet-like plates, 

 forming, by their union, a kind of sucker, which is received in a sheath which takes 

 the place of the labium, and is either cylindrical or conical, and articulated, in the 

 form of a beak {rostrum), or membranous and fleshy, inarticulated, and terminated 

 by two lips (proboscis). The labrum is triangular and arched, covering the base of 

 the sucker. 



In the second of these modifications, the liibrum and mandibles are nearly obsolete, 

 or extremely small. The labium is no longer a detached piece, and is only distin- 

 guished by the presence of a pair of palpi, of which it is the sujiport. The maxillae 

 have acquired a very great length, and are transformed into two tubular threads, which, 

 uniting by the edges, forms a kind of proboscis which is rolled up in a spiral manner, 

 and is named the tongue, but which, to avoid misconception, it would be preferable to 

 term the spirignatha : its interior presents three canals, of which the middle one forms 



• AccorHiiiff to whnt I hix-c salil in the introductury obscrvntiotis 

 upon the ArticuliitJiiii genertil, [ cuiisiclfr Ilic lower lip lo be but ri iiiodi- 

 6catiiHi of the second maxill(C of the deinpod Crustaeen, conibiiUMi 

 with their totiKue (languette). The jfradmtl thmiiccs wltich tnVp ]il..ce 

 in the form of these orjfans, in the (^rustncoa, Arachnida, and Mvria- 

 poda. naturally lead to this supposition. In this hypothesis, the six 

 thoracic lejfs must be annloijous to the foot-jaws of the Crabs; and as 

 has been shown, in llie crustaceous genus Apus. Moreover, the five 



anterior abdominal se|;njrnts of he.xapod insects will represent ihe 

 scifnients which bi-ar the true lens in the decapod Crustacea, or the 

 third and four succeedini; seKmeiits of the aniphipod and isopod 

 Crustacea. The various works published in respect to the thorax of 

 insects will necessarily require revision when this part of the body is 

 compared throughout the three annulosc classes, its nomenclature 

 being far from fixed in this respect. 



