i DOCKIPTION OF PARTS. 



Tito external ooreiing of inseets b quite hard : it is called integument, or crust, and 

 •uppliee the place of the internal skeleton, and is the part to which the muscles are at- 

 iMhed. It if somewhat horny, or corneous, but varies considerably in this respect in the 

 limmml qiedes : in certain beetles it is hard and inflexible ; while in others, it is soft and 

 onHe flexible. It resembles the true skin of animals in its divisibility into three layers, an 

 epidermis, a rete mucosum,and a leathery tunic called the corium or dermis, the true skin. 

 This oater integument is composed chemically of phosphate of lime and magnesia ; but, 

 iHut is interesting, it is found to contain a peculiar substance, termed chitine, which is 

 insoloble in potash. Phosphate of iron, albumen, and a peculiar coloring matter, are also 

 unong the substances composing this iutegumeiil. 



The shape of the head is variable, but the spherical form predominates. The integument 

 forms a kind of box, with an aperture in front, through which the organs of the mouth 

 maybe thrust. The posterior part furnishes a place and attachments for the muscles which 

 move the head upon the thorax. The eyes are large, usually, and occupy the lateral parts 

 of the head. The external parts of the head have received dififerent names. The epicranium 

 is that portion which extends from the eyes backwards. In front of the epicranium, is the 

 fticehead. The clypeus is the margin in front above the mouth. Sometimes the whole region 

 in front of the eyes is called the face. The inferior parts of the box enclosing the head has 

 also its spaces, which have received distinct names, as gula, or throat, which lies imme- 

 diately behind the margin of the lower lip, and extends back to the prothorax. The cheeks 

 are situated upon the sides of the head, from the eyes downwards to the mouth. The an- 

 teante are situated between the angle of the mouth and the eyes : they have a subglobose 

 Joint at the base, upon which they move, and which is placed in a kind of socket ; this is 

 sometimes called a tm-vlus, 



.The mouth, as may be supposed, is constructed so as to answer the ends designed, and 

 it is either suctorial or manducatory, masticating : if the food is fluid, it is suctorial ; if 

 solid, it has jaws for mastication. In the mandibulate or masticating, there is perfect free- 

 dom of motion ; in the suctorial or haustellate {hamtellata), the parts are more or less 

 soldered together, so as to form a tube for the transmission of fluids. The terms haustdlata 

 and mandibulata apply, therefore, to two great classes of insects, one of which subsists on 

 the juices of plants and animals, which they obtain by suction ; the others, the masticating, 

 subsist on solid substances. Animals destined to obtain food by modes so apparently distinct, 

 ftiniish many distinctive characters of importance. The labrum is the most anterior part 

 sssn from above ; it covers the mouth, and is united by a membranous hinge to the cly- 

 paos : it is employed in retaining the food in the mouth during mastication ; it is, there- 

 fcre, a true upper lip, but of a variable form. Mastication is performed by the mandibles, 

 wl)ich are two strong jaws that move laterally, and consist of wedge-shaped or triangular 

 pieces more or less elongated, and placed immediately below the labrum. These organs are 

 also called upper jaws : they move like the blades of scissors. Their inner edge is fre- 



