MOTIONS OF INSECTS. 475 



greater diameter than before, and the claws stand erect with their points 

 outwards. TIjus they can lay stronger hold of the plane of position.^ 



The number of these prolegs varies in different species and families. 

 In the numerous tribes of saw-flies (^Serrifera), the larvae of which resem- 

 ble those Lepidoptcra, and are called by Reaumur spurious caterpillars 

 (Jausses chenilles), one family (^Lophyrus) has sixteen prolegs; a second 

 (Hylotoma, &.c.) fourteen; another (^Tenthredo F.) twelve; and a fourth 

 {Lyda) none at all, having only the six perfect legs. The majority of 

 larvas of Lepidopfera have ten prolegs, eight being attached, a pair on each, 

 to the sixth, seventh, eighth, and ninth segments of the body, and two to 

 the twelfth or anal segment.^ The caterpillar of the puss-moth (^Cerura 

 Vinuld) and some others, instead of the anal prolegs, have two tails or 

 horns. A hemigeometer, described by De Geer, has only six intermediate 

 prolegs, the posterior pair of which are longer than the rest, to assist the 

 anal pair in supporting the body in a posture more or less erect.^ Other 

 hemigeometers, of which kind is the larva of Plusia Gamma, have only 

 six prolegs, four intermediate and two anal. The true geometers or sur- 

 veyors {Geometm) have only two intermediate and two anal prolegs. 

 Many grubs of Coleoptera, especially those of Staphylinidce, Silphida, 

 &c., which are long and narrow, are furnished with a stiff joint at the 

 anus, which they bend downwards and use as a prop to prevent their 

 body from trailing. This joint, though without claws, may be regarded 

 as a kind of proleg, which supports them when they walk^ ; and probably 

 may assist their motion by pushing against the plane of position. 



With respect to the larvae that have only perfect legs, having just given 

 you an account of these organs, I have nothing more to state relating to 

 their structure. I shall therefore now consider the motions of pedate 

 larvae, under the several heads of walking or running, jumping, climbing 

 and swimming. 



Amongst those that walk, some are remarkable for the slowness of 

 their motion, while others are extremely swift. The caterpillar of the hawk- 

 moth of the Filipendula (Zygena Filipendulcz) is of the former descrip- 

 tion, moving in the most leisurely manner ; while that of Apatela lepo- 

 rina, a moth unknown in Britain, is named after the hare, from its great 

 speed. The caterpillar of another moth, the species of which seems not 

 to be ascertained, is celebrated by De Geer for the wonderful celerity of 

 its motions. When touched it darts away backwards as well as forwards, 

 giving its body an undulating motion with such force and rapidity, that it 

 seems to fly from side to side.^ Cuvier observes, that the grubs of some 

 coleopterous and neuropterous insects, which have only the six perfect 

 legs, by means of them lay hold of any surrounding object, and, fixing 

 themselves to it, drag the rest of their body to that point ; and that those 

 of many Capricorn beetles and their affinities (but that of Callidium viola- 

 ceum, is an apode^) have these legs excessively minute and almost nothing ; 

 that they move in the sinuosities which they bore by the assistance of 

 their mandibles, with which they fix themselves, and also of several dorsal 

 and ventral tubercles, by which they are supported against the sides of 



» Lyonet, 82. t. iii. f. 10—16. « Ibid. t. i. f. 4. 



» De Geer, i. 379. t. xxv. f. 13. 



* De Geer, i. 12. 40. t. i. f. 27. q. t. vi. f. 11. e. 



» De Geer, i. 424. • Eirby in Linn. Trans, v. 258. 



