578 INSECTS AND AKACHNIDA. 



confirmation, from the presence of a similar apparatus, on a far 

 larger scale, on the foot of the Dytisous (Fig. 295, a). The first 

 joints of the tarsus of this insect are widely expanded, so as to 

 form a nearly circular plate ; and this is provided with a very 

 remarkable apparatus of suckers, of which one disk (a) is ex- 

 tremely large, and is furnished with strong radiating fibres, a 

 second (6) is a smaller one formed on the same plan (a third, of 

 the like kind, being often present), whilst the greater number 

 are comparatively small tubular club-shaped bodies, each having 

 a very delicate membranous sucker at its extremity, as seen on a 

 larger scale at b. These last seem to resemble the hairs of the 

 Fly's foot in every particular but dimension ; and an intermediate 

 size is presented by the hairs of many beetles, especially Curcu- 

 lionidee. The feet of Caterpillars difl:er considerably from those 

 of perfect Insects. Those of the first three segments, which are 

 afterwards to be replaced by true legs, are furnished with strong 

 horny claws; but each of those of the other segments, which are 

 termed "pro-legs," is composed of a circular series of compara- 

 tively slender curved booklets, by which the catei-pillar is enabled 

 to cling to the minute roughnesses of the surface of the leaves, 

 &c., on which it feeds. This structure is well seen in the pro- 

 legs of the common Silk-worm. 



398. Stings and Ovipositors. — The Insects of the order Hymen- 

 optera are all distinguished by the prolongation of the last seg- 

 ment of the abdomen into a peculiar organ, which, in one division 

 of the order, is a " sting," and in the other is an " ovipositor," 

 — an instrument for the deposition of the eggs, which is usually 

 also provided with the means of boring a hole for their reception. 

 The former group consists of the Bees, Wasps, Ants, &c. ; the 

 latter of the Saw-flies, Gall-fiies, Ichneumon-flies, &c. These 

 two sets of instruments are not so unlike in structure, as they 

 are in function. The " sting" is usually formed of a pair of 

 darts, beset with barbed teeth at their points, and furnished at 

 their roots with powerful muscles whereby they can be caused 

 to project from their sheath, which is a horny case formed by the 

 prolongation of the integument of the last segment, slit into 

 two halves, which separate to allow the protrusion of the sting ; 

 whilst the peculiar "venom" of the sting is due to the ejection, 

 by the same muscular action, of a poisonous liquid, from a bag 

 situated near the root of the sting, which passes clown a canal 

 excavated between the darts, so as to be inserted into the punc- 

 ture which they make. The stings of the common Bee, Wasp, 

 and Hornet, may all be made to display this structure without 

 much difiiculty in the dissection. The " ovipositor" of such in- 

 sects as deposit their eggs in holes ready made, or in soft 

 animal or vegetable substances (as is the case with the leJmeu- 

 monidce), is simply a long tube, which is enclosed, like the stingy 

 in a cleft sheath. In the Gall-flies [Cynipidce), the extremity of 

 the ovipositor has a toothed edge, so as to act as a kind of saw, 



