MOTIONS OF INSECTS. 



267 



him suspect that it acted like a cupping-glass, and so pro- 

 duced the adhesion. 1 This circumstance affords another 

 proof that the foot-cushions in the Orthoptera may act the 

 same part ; they appear to be vesicular ; and in numbers of 

 specimens, after death, I have observed that they become 

 concave, particularly in Acrida viridissima. 



In Cimbex, and others amongst the saw-fly tribes, the claw- 

 sucker is distinguished by this remarkable peculiarity, that 

 its upper surface is concave 2 , so that before it is used it must 

 be bent inwards. Besides these, at the extremity of each 

 tarsal joint these animals are furnished with a spoon-shaped 

 sucker, which seems analogous to the cushions in the Gryllina, 

 Locustina, &c. ; and, what is more remarkable, the two spurs 

 (calcaria) at the apex of the shanks have likewise each a mi- 

 nute one. 3 Various other insects of this order have the 

 claw-suckers. Amongst others the common wasp (Ves-pa 

 vulgaris) is by these enabled to walk up and down our glass 

 windows. 



We learn from De Geer that several mites (to finish with 

 the Aptera) have something of this kind. Among these is 

 the cheese-mite {Acarus siro) ; its four fore feet being ter- 

 minated by a vesicle with a long neck, to which it can give 

 every kind of inflexion. When it sets its foot down, it en- 

 larges 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. 4 The itch Acarus {A. scabiei) is si- 

 milarly circumstanced. Ixodes Ricinus and Reduvius have 

 also these vesicles — which are armed with two claws — on all 

 their feet. 5 



I am next to consider those climbers that ascend and de- 

 scend, and probably maintain themselves in their station, by the 

 assistance of a secretion which they have the power of pro- 

 ducing. 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 



i De Geer, iii. 7. 2 Philos. Trans. 1816, t. xix. f. 3, 4. 



3 Philos. Trans. 1816, t. xix. f. 1—9. 



4 De Geer, vii. 91. t. v. f. 6, 7. 



5 Ibid. 96. t. v. f. 13, 14, 17. 19. t. vi. (.2.5. 



