578 INSECTS AND ARACHNID A. 



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

 larger scale, on the foot of the Dytiscus (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 (b) 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- 

 lionidpe. The feet of Caterpillars differ 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 caterpillar 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-flies, 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 down 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 difficulty 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 Ichneu- 

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

 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, 



