488 Div. 3. ARTIOULATA.— INSECTA. 



Class 3. 



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

 and a valuable memoir is published in the first volume of the Transactions of the Entomoloffical Society of 

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

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

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

 Sciences, a memoir, in which he announces the existence of branchiae in the Machilis polypoda, 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 

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

 the inferior Crustacea. M. Guerin has stUl more recently figured them in his Jconographie.'] 



THE THIRD ORDER OF INSECTS,— 



PARASITA, Latr., (Anopluba, Leach),— 



(Or the Lice), thus named from its habits, have only six legs, and are apterous, hke the Thysa- 

 noura; but the abdomen is destitute of articulated and moveable appendages. Their organs 

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

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

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

 according to Linnajus, the single genus 



Pediculus, 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 very 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 which they pass their Uves, 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 especially the case in respect to the common Body Louse, in the disease named phthiriasisf, an(^ 

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

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

 kinds of Lice. They generally crawl very slowly. 



Some species form the tribe Pediculidea of Leach, including 



Pediculus, De Geer, which has, in the place of a mouth, a very 

 small tubular tubercle, situateii at the anterior extremity of the 

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

 The tarsi are composed of a joint, in size nearly 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 which I have examined, I have only seen two ocelli, one on 

 each side. Man supi)oits three kinds, their eggs being known under 

 K the name of Nits. The Body Louse {P. humantis corporis, De Geer), 

 white, without spots, which multiplies excessively in the disease 

 called phthiriasis, and the Head Louse (P. humanus capitis, DeGecr), 

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

 Fig. 49.— n. The Common Louse ; i. nin({nific.i ; r, one uf pspecjally of children, form Leach's genus Pfrf(c;//M*, having the 

 the leg« magnified i rf, eggs ;<•. 'l'"o ""'IS'"'"^''- ... , , , , „.,. r. _,• , i ■ t • 



thorax quite distinct from the abdomen. ^hePedicuhts pubis, lAwn., 



or Morpeon [Crabs, or Crab-lice], forms Dr. Leach's genus PMIiirus, Laving the thorax very short, nearly con- 



• (LBlreille. in his eUboratc memoir upon the orRanization of the 1 Burmeister, collect in great numbers upon the skin at parlicnlar parts 

 Thysanoura, was unable tniletectthp ordinary spiracles for brcalhint!.] I of the breast, neck, and back, where the epidermis peels off. Bur 



t [Alt, in his Duiert::H<) de Phlhiriati, Bonn, ISiO, attributes this meister attributes their appearance to equivocal geueraUoD. 

 disease to another gpecies (/*. tabeicentium). which, according to | 



