MOTIONS OP INSECTS. 



233 



and the claws stand erect with their points outwards. Thus 

 they can lay stronger hold of the plane of position. 1 



The number of these prolegs varies in different species and 

 families. In the numerous tribes of saw-flies (Serrifera), the 

 larvae of which resemble those Lepidoptera, and are called by 

 Reaumur spurious caterpillars (fausses 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 larvae of Lepidoptera have ten prolegs, eight being attached, 

 a pair on each, to the sixth, seventh, eighth, and ninth seg- 

 ments of the body, and two to the twelfth or anal segment. 2 

 The caterpillar of the puss-moth (Cerura Vinula) and some 

 others, instead of the anal prolegs, have two tails or horns. A 

 hemigeometer, described by De Geer, has only six intermedi- 

 ate 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. 3 Other hemigeometers, of which kind is 

 the larva of Plusia Gamma, have only six prolegs, four inter- 

 mediate and two anal. The true geometers or surveyors 

 ( Geometrce) have only two intermediate and two anal prolegs. 

 Many grubs of Coleoptera, especially those of Staphylinidce, 

 Silphidce, &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 4 ; 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, climb- 

 ing and swimming;. 



Amongst those that walk, some are remarkable for the 

 slowness of their motion, while others are extremely swift. 



1 Lyonet, 82. t. iii. f. 10—16. 2 Ibid. t. i. f. 4. 



3 De Geer, i. 379. t. xxv. f. 1. 3. 



4 De Geer, i. 12. 40. t. i. f. 27. q. t. vi. f. 1 1. e. 



