332 MOTIONS OF INSECTS. 
We learn from De Geer that several mites (Acaride), 
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 en- 
tirely disappears. This vesicle is between two claws?.— 
The itch acarus (A. Scabie7, L.)is similarly circumstanced. 
—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 
(Araneide), 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 biarti- 
culate tarsi, to enable them to do it—can also walk against 
a We GeeraviiOl.2.ve76. 7. 
b Ibid. 96— ¢. v.f. 13, 14, 17,19. te vif 2,5. 
© Vou, I. 4th Ed. 407. 
