MOTIONS OF INSECTS. 333 



mals, although they have no suckers or other appa- 

 ratus — except the hairs of their legs and the three 

 claws of their biarticulate tarsi, to enable them to do it 

 — can also walk against gravity, both in a perpendicular 

 and a prone position. Dr. Hulse, in Ray's Letters^ 

 seems to have furnished a clue that will very well 

 explain this. I give it you in his own homely phrase. 

 "They," spiders, " will often fasten their threads in 

 several places to the things they creep up; the manner 

 is by beating their bums or tails against them as they 

 creep along*." Fixing their anus by means of a web, the 

 anterior part of their body, when they are resting, we 

 can readily conceive, would be supported by the claws 

 and hairs of their legs ; and their motion may be ac- 

 complished by alternately fixing one and then the other. 

 But you will remember I give you this merely as con- 

 jecture, having never verified it by observation. 



It may not be amiss to mention here another apte- 

 rous insect that reposes on perpendicular or prone sur- 

 faces, without either suckers or any viscous secretion 

 by which it can adhere to them. I mean the long-legged 

 or shepherd spiders (Phalangium, L.). The tarsi of 

 these insects are setaceous and nearly as fine as a hair, 

 consisting sometimes of more than forty joints, those 

 toward the extremity being very minute, and scarcely 

 discernible, and terminating in a single claw. These 

 tarsi, which resemble antennas rather than feet, are ca- 

 pable of every kind of inflexion, sometimes even of a 

 spiral one. These circumstances enable them to ap- 

 ply their feet to the inequalities of the surface on whicli 

 they repose, so that every joint may in some measure 



' 63. 



