MOTIONS OF INSECTS. 273 



is obliged to spin, at certain intervals, little hillocks or 

 steps of silk ; of which it then lays hold by them, and 

 so drags itself along. 



Besides their mandibular hooks, some of these grubs 

 supply the want of legs by means of claws at their anus. 

 Thus that of the flesh-fly, Ray tells us in the place just 

 quoted, pushes itself by the protruded spines of its tail. 

 The larva also of a long-legged gnat (Limnobia repli- 

 cata\ which in that state lives in the water, is furnished 

 with these anal claws, which, in conjunction with its 

 annular tension and relaxation, and the hooks of its 

 mouth, assist it in walking over the aquatic plants". 



A remarkable difference, according to their station, 

 obtains in the bots of gad-flies (CEstrida) ; those that 

 are subcutaneous ( CuticolcK^ Clark) having no unguiform 

 mandibles; while those that are gastric (Gastricola, 

 Clark), and those that inhabit the maxillary sinuses of 

 animals (Cavicolte, Clark), are furnished with them. In 

 this we evidently see Creative Wisdom adapting means 

 to their end. For the cuticular bots having no plane 

 surface to move upon, and imbibing a liquid food, in 

 them the mandibular hooks would be superfluous. But 

 they are furnished with other means by which they can 

 accomplish such motions, and in contrary directions, as 

 are necessary to them ; the anterior part of each segment 

 being beset with numbers of very minute spines, not 

 visible except under a strong magnifier, sometimes ar- 

 ranged in bundles, which all look towards the anus ; and 

 the posterior part is as it were paved with similar hooks, 

 but smaller, which point to the head. Thus we may 

 conceive, when the animal wants to move forward, that 

 a De Geer, vi. 355. 



VOL. II. T 



