186 



a cylindrical and elongated form ; but various modifications 

 occur, some larvae being flattened, others oval, some short 

 and thick, others having the segments very irregular, warty, 

 spinose, or hirsute. The three anterior segments are, how- 

 ever, ordinarily distinguished by each having on its inferior 

 surface a pair of short scaly legs, composed of fom' or five 

 joints, which are analogous to those of which the legs of the 

 perfect insect are composed, and generally terminated by a 

 small claw (fig. 22). In many larvae, as I have indicated in 

 the table given above, these are the only legs with which the 

 insect is furnished, although it rarely occm-s that these ai-e 

 25 



wanting, the organs of motion being the merely rudimentai 

 prolegs. These prolegs are thick, and of a membranous 

 construction, so that, unhke the true articulated legs, which 

 are capable of motion only at the articulations of the 

 joints, these are completely flexible. They are exclusively 

 adapted to the insect whilst it remains in the larva state, 

 there being nothing at all analogous to them on their arrival 

 at the perfect state. These legs are furnished at the extre- 

 mity with a multitude of minute bent hooks, which are em- 

 ployed by the larva in retaining its situation, upon whatever 

 substance it may happen to be placed, with very great firm- 

 ness (figs. 23 and 24). These prolegs are very variable both 

 in their structm*e and situation, as also in their number, vary- 

 ing from two to eighteen. These variations afford grounds 

 for classifications of the larvae, but which it would be tedious 

 to detail without entering more fidly into minute particulars 

 than my space will allow. The terminal segment of the 



