INSECTA. 
488 
[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 Entomological Society of 
London, upon the Irish species, by R. Templeton, 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 still more recently figured them in his Jconographied\ 
THE THIRD ORDER OF INSECTS — 
PARASITA, Latr., (Anoplura, Leacli),— 
(Or the Lice), thus named from its habits, have only six legs, and are apterous, like the Thysa- 
noura ; 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 tubercle, inclosing a retractile 
sucker, or two membranous lips, close together, with two hooked mandibles. They compose, 
according to Linnaeus, 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 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 especially the case in respect to the common Body Louse, in the disease named phthiriasisf, and 
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, situated 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 supports three kinds, their eggs being known under 
the name of Nits. The Body Louse (P. humanus corporis, De Geer), 
white, without spots, which multiplies excessively in the disease 
called phthiriasis, and the Head Louse (P. humanus capitis, De Geer), 
ashy colour, with darker spots, found only on the head of man, and 
Fig. 49.— ^ 2 , The Common Louse ; 6, mapified ; c, one especially of children, form Leach’s genus Pediculus, liscvm^ the 
the legs magnified ; d, eggs ; e, ditto magnified. i j « j & 
thorax quite distinct from the abdomen. The Pediculus pubis, Linn., 
or Morpeon [Crabs, or Crab-lice], forms Dr. Leach’s genus Phthirus, having the thorax very short, nearly con- 
* [Latveille, in his elaborate memoir upon the organization of the 1 Burmeister, collect in great numbers upon the skin at particular parts 
Thysaiioura, was unable to detect the ordinary spiracles for breathing.] 1 of the breast, neck, and back, where the epidermis peels off. Bur- 
t [Alt, in his Dissertatio de Phthirinsi, Bonn, 1820, attributes this 1 meister attributes their appearance to equivocal generation, 
disease to another species (T. tahescentium) , which, according to ] 
