138 STATES OF INSECTS. 



gular prolegs before described a of another gnat ( Tany- 

 pus maculatus Meig., Tipula De Geer). The case-worms 

 (Trichopiera K.) and some others, have two prolegs at 

 the anus, each furnished with a single claw b . 



ii. The prolegs deprived of claws are found in the 

 larva of the Hymenopterous tribe of saw-flies ( Tenthredo 

 L.), in those of some Lepidoptera (Hepialus F. &c), and 

 in some few Coleopterous and Dipterous genera. Those 

 of the former are of the shape of a truncated cone, and 

 resemble the second class of unguiculate prolegs, except 

 in the defect of claws. In the latter they are a mere re- 

 tractile nipple-like protuberance, in some species so small 

 as scarcely to be perceptible. In all they aid in progres- 

 sive motion ; but it is by laying hold of surfaces, and so 

 enabling the body more readily to push itself forward by 

 annular contraction and dilatation, and not by taking 

 steps, of which all prolegs are incapable : to assist in this 

 purpose the protuberance sometimes secretes a gluten c , 

 which supplies the place of claws. Some larvae have the 

 power of voluntarily dilating certain portions of the un- 

 derside of their body, so as to assume nearly the shape 

 and to perform the functions of prolegs. In a Coleopte- 

 rous (?) subcortical one from Brazil, before alluded to, 

 there are four round and nearly flat areas in each ventral 

 segment of the abdomen, but the last very little raised 

 above the surface, and rough, somewhat like a file; and 

 besides these, the base of the anal segment has ten of 

 these little rough spaces, but of a different shape, being 

 nearly linear, placed in a double series, five on each side. 

 Doubtless these may be regarded as a kind of prolegs^ 



" See above, Vol. II. p. 278. Dc Geer ubi supr. 376. 



! ' Rcaura. iv, 181. t, xv, f, 12, c c. c De Geer v. 203. 



