183 INSECTA. 



[These insects liave been greatly neglected by naturalists, but Dufour has described various species; 

 and a valuable menioir is published in tlie first volume of the Traiuaciions of the Entomological Society of 

 London, upon the Irish species, by K. Templetou, Escp, R.A., comprising several new genera, and accom- 

 panied by beautiful figures. Some of Ins species, however, appear to me to be established upon the 

 immature states of these insects- M. Guerin has also very recently presented to the Aeademie des 

 Sciences, a memoir, in whicli he announces the existence of branchiae in the Machilis -polyjyoda, Latr. ; 

 the breathing apparatus* consisting of minute plates placed under the abdominal segments, and by the 

 side of those appendages which are compared to the false legs of the Crustacea. They are inclosed in 

 httle membranous bags, of a similar organization to those of the respiratory organs of a great number of 

 the inferior Crustacea. M. Guerin has still more recently figured them in his Iconographies^ 



THE THIRD ORDER OF INSECTS,— 



PARASITA, Latr., (Anoplura, Leach),— 



(Or the Lice), tlius named from its habits, have only six legs, and are apterous, like the Tbysa- 

 nom'a; but the abdomen is destitute of articulated and moveable appendages. Their organs 

 of sight merely consist of four or two small ocelli. The mouth is, for the most part, internal, 

 and exhibits, on the outside, either a snout or fleshy porrected tuberclej inclosing a retractile 

 sucker, or two membranous lips, close togethei', with two hooked mandibles. They compose, 

 according to LiuuEcus, the single genus 



Pediculits, Linn. 

 The body is flattened, nearly transparent, divided into eleven or twelve distinct segments, of which 

 three, forming the trunk, have a pair of legs attached to each. The first of these segments often forms 

 a kind of corselet. The spiracles are very distinct. The antennae are short, of equal thickness through- 

 out, composed of five joints, and often inserted in an excavation. Each side of the head exhibits one 

 or two minute ocelli. The legs are short, and terminated by a ver;^ strong nail, or by two opposing 

 hooks, whereby these animals easily fasten themselves to the hairs of quadrupeds or feathers of birds, 

 of which they suck the blood, and upon the body of vp hi eh they pass their lives, and there multiply, 

 attaching their eggs to those cutaneous appendages. Their generations are numerous, and succeed each 

 other very rapidly. Particular causes, unknown to us, are very favourable to their production; and 

 this is es]iecially the case in respect to the common Body Louse, in the disease named phthiriasist, and 

 also in infancy. They always live upon the same quadrupeds and birds, or at least upon the animals 

 of those classes whicli have analogous characters and habits. One bird, however, often supports two 

 kinds of Lice. They generally crawl very slowly. 



Some species form the trilie Pcdiciilidea of Leach, including 



Ped/culiis, De Geer, which has, in the place of a mouth, a very 

 smalt tubular tubercle, situated at the auterior extremity of the 

 head, in the furm of a snout, and inclosing, in inaction, a sucker. 

 The tarsi are composed of a joint, in size uearly equal to the tibia, 

 and terminated by a very strong hook, folding upon a prominent 

 tooth at the extremity of the tibia, acting; with it as a pincers. In 

 those whicli I have examined, I have only seen two ocelU, one on 

 J Vj) v' 1 ' ■■ ' I'l ~~'{ yr^k- ^\~ '^'**^^^ ^^'^^' "^"^''*" supports three kinds, their egg^s being known under 



^- V^'^TiT I /- 'k V^ the name of Nits. The Body Louse {P. humanus corporis, De Geer), 



'\'-.\y white, \\ithont spots, which multiplies excessively in the disease 

 '^ ^^ i;ailed phthiriasis, and the Head Louse (P. hmnanus capitis, BeGeer), 

 ashy colour, with darker spots, found only on the head of man, and 

 I'li'i'ii^iT'^ °^ especially of children, form Leach's genus Pediadm, having the 

 thorax quite distinct from the abdomen. The Pcdlcnhis jnibis, Linn., 

 or Morpeon [Crabs, or Crab-bee], forms Dr. Leach's genus JP/i!^/;/>«i', having the thorax very short, nearly con- 



• [Lalreille. !n Ins elRbomte memoir upon the orf,'anization of the 

 'I'liysnnoura.wfts anable ro'lciectihe ordinary .iplracU-;! for breatliirt;.] 



t [Alt, In hi'i !>b^,-r<,:nr, de Phthiriasi, Botm, ISi^O, attributes tliis 

 .iiie/ise tu anoUiur 6f.ccie» {P. tuOncnifium). wUicl), according: lo 



