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 a . 

 The itch Acarus (A. Scabiei] is similarly circum- 

 stanced. Ixodes Ricinus and Reduvius have also these 

 vesicles which are armed with two claws on all their 

 feet b . 



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 

 (Araneid<z\ 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 c ; 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 



a DeGeer, vii. 91. t.v.f. 6,7. 



b Ibid. 96-. t. v.f. 13, 14, 17, 19. t. vi./. 2. 5. 



c VOL. I. 405. ' 



