328 MOTIONS OF INSECTS. 



with the Aptera, have something of this kind. Among 

 these is the cheese-mite {Acarus Siro) : 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' en- 

 tirely disappears. This vesicle is between two claws =•. 

 — The itch Acarus {A. Scuhiei) is similarly circum- 

 stanced. — Ixodes Ricinus and Reduvius have also these 

 vesicles — which are armed with two claws — on all their 

 feet ^ 



I am next to consider those climbers that ascend and 

 descend, and probably maintain themselves in their sta- 

 tion, by the assistance of a secretion which they have the 

 power of producing. You will immediately perceive 

 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 some- 

 times guiding their thread *= ; but when their motion is 

 suspended, they are bent inwards. These animals, al- 

 though they have no suckers or other apparatus — except 

 the hairs of their legs and the three claws of their bi- 

 articulate tarsi, to enable them to do it — can also walk 



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



" Ibid. 96—. /. v./. in/ll, ]7, 19. /. vi./. 2. 5. 



• Vol.. I. 405—. 



