332 MOTIONS OF INSECTS. 



wasp ( Vespa vulgaris) is by tliese enabled to walk up 

 and down our glass windows. 



We learn from De Geer that several mites (Aca-- 

 ridce)y to finish with the Aptera, have something- of this 

 kind. Among these is the cheese-mite {Acarus Siro, 

 F.) : its four fore feet being terminated by a vesicle 

 with a long neck, to which it can give every kind of 

 inflexion. When it sets its foot down, it enlarges and 

 inflates it ; and when it lifts it up, it contracts it so that 

 the vesicle almost entirely disappears. This vesicle is 

 between two claws ^. — The itch acarus (A. Scabiei, L.) 

 is similarly circumstanced. — Ixodes Ricinus and Re- 

 dwoius have also these vesicles — which are armed with 

 two claws — on all their feef^. 



I am next to consider those climbers that ascend and 

 descend, and probably maintain themselves in their 

 station, by the assistance of a secretion which they have 

 the power of producing. You will immediately per- 

 ceive that I am speaking of the numerous tribes of 

 spiders (Araneidce), which, most of them, are endowed 

 with this faculty. Every body knows that these insects 

 ascend and descend by means of a thread that issues 

 from them ; but perhaps every one has not remarked 

 — when they wish to avoid a hand held out to catch 

 them, or any other obstacle — that they can sway this 

 thread from the perpendicular. When they move up 

 or down, their legs are extended, sometimes gathering 

 in and sometimes guiding their thread*^; but when their 

 motion is suspended, they are bent inwards. These ani- 



" DeGeer,vii. 91. ^v. /.6,7, 



»• Ibid. 96— t. V. /. 13, 14, 17, 19, t. v j. /. 2, 5. 



« Vol. I. ?(iEd. 407. 



