320 MOTIONS OF INSECTS. 
surface on which they stand, and unbending it with force, 
they are out of your reach before your finger can come 
near them. One of them, S. fuscus, besides the caudal 
fork, has a very singular organ, the use of which is to 
prevent it from falling from a perpendicular surface, on 
which they are often found at a great height from the 
ground. Between the ends of the fork there is an ele- 
vated cylinder or tube, from which the animal, when ne- 
cessary, can protrude two long, filiform, flexible trans- 
parent threads covered with a slimy secretion. By these, 
when it has lost its hold, it adheres to the surface on 
which it is stationed?. Another insect related to the 
common sugar-louse, and called by Latreille Machzlis 
polypoda (Lepisma, ¥.), in some places common under 
stones”, has eight pair of springs, one on each ventral 
segment of the abdomen, by means of which it leaps to 
a wonderful distance, and with the greatest agility. 
Climbing is another motion of insects that merits par- 
ticular consideration: since, as this includes their power 
of moving against gravity—as we see flies and spiders 
do upon our ceilings, and up perpendicular surfaces | 
even when of glass—it affords room for much interest- 
ing and curious inquiry. Climbing insects may be di- 
vided into four classes.—Those that climb by means of 
their claws ;—those that climb by a soft cushion of dense 
hairs, that, more or less, lines the underside of the joints 
of their tarsi, the claw-joint excepted ;—those that climb 
by the aid of suckers, which adhere (a vacuum being pro- 
duced between them and the plane of position) by the 
pressure of the atmosphere ;—and those that are enabled 
* De Geer, vii. 38—. ¢. ii. f. 10. rr. 
> This insect abounds at East Farleigh, near Maidstone. 
