8 DESCRIPTION OF PARTS. 



The external covering of insects is quite hard : it is called integument, or C7tist, and 

 supplies the place ..f the internal skeleton, and is the part to which the muscles are at- 

 tached. It is somewhat horny, or corneous, but varies considerably in this respect in the 

 different species : in certain beetle.- it is hard and inflexible ; while in others, it is soft and 

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

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

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

 what is interesting, it is found to contain a peculiar substance, termed ckitine, which is 

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

 anions the substances composing this integument. 



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 furmshes 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 different names. The epicranium 

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

 forehead. The clypcus 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- 

 tenna? 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 torulus. 



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 mandilnilate or masticating, there is perfect free- 

 dom of motion ; in the suctorial or haustellate (hauste/lata), the parts are more or less 

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

 and mandibuhita 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, 

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

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

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

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

 which are two strung 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- 



