INSECTS. 219 



der also the jaws form small compressed valves, and the chin 

 becomes a kind of cylindrical or conical tube. All these parts, 

 as well as the labium, are often much elongated, and compose to- 

 gether a species of trunk or proboscis, which Illiger names pro- 

 muscis, and which Latreille calls a spurious proboscis ; and 

 in regard to this organ M. Lamarck considers the Hymenopte- 

 ra as intermediate between the gnawers and the suckers. 



Among the insects which feed on fluids, or which extract 

 their food by suction, the organs of manducation appear under 

 two modifications. In the first, the mandibles and jaws are 

 replaced by minute laminae in the form of setae, composing 

 by their union a kind of sucker (haustellum) which is received 

 into a sheath, the substitute for a lip, either cylindrical, conical, 

 or jointed, termed the rostrum or beak in the Hemiptera ; or 

 membranous and fleshy, terminated by two lips, termed the 

 trunk or proboscis in the Diptera. The labrum is triangular 

 or conical, and covers the base of the sucker. In the second 

 modification the mandibles are excessively small, and in the 

 form of a tubercle more or less triangular, furnished with ci- 

 liae on the internal margin ; the lip is only distinguished by 

 the presence of palpi ; the jaws acquire an extraordinary length, 

 and unite to form a proboscis or tongue (lingua) rolled up in a 

 spiral form. Interiorly this tongue is provided with three ca- 

 nals, of which the intermediate one is the conduit of the nutri- 

 tive juices ; and at the base of each of the filaments is a minute 

 palpus. The mouth of the Lepidoptera is an instance of this 

 construction. 



The trunk or thorax is that part of the body which unites 

 the head to the abdomen, and to which are attached the organs 

 of locomotion. It is formed of three segments, each with a 

 pair of feet ; but in the winged insects the upper sides of the last 

 two segments also form points of attachment for the wings. The 

 term thorax has been given to the upper surface of the trunk, 

 and that of breast to the opposite face below. The middle part 

 of the breast between the feet, (presenting in many, either be- 

 fore or behind, a projection in the form of a horn or point) is 

 the sternum ; and the portion between the attachment of the 

 wings, generally triangular, and sometimes very large, is named 

 the shield or scutellum. The anterior segment of the thorax in 

 a great many winged insects is much larger than the other seg- 



