256 



MOTIONS OF INSECTS. 



form than Podura, are so excessively agile that it is almost 

 impossible to take them. Pressing their spring against the 

 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. fascus, 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 elevated cylinder or tube, from which 

 the animal, when necessary, can protrude two long, filiform, 

 flexible transparent threads covered with a slimy secretion. 

 By these, when it has lost its hold, it adheres to the surface 

 on which it is stationed. 1 Another insect related to the 

 common sugar-louse, and called by Latreille Machilis poly- 

 poda, in some places common under stones' 2 , 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 particular 

 consideration : since, as this includes their power of moving 

 against gravity — as we see flies and spiders do upon our ceil- 

 ings, and up perpendicular surfaces even when of glass, it 

 affords room for much interesting and curious inquiry. 

 Climbing insects may be divided 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 ex- 

 cepted ; those that climb by the aid of suckers, which adhere 

 (a vacuum being produced between them and the plane of 

 position) by the pressure of the atmosphere ; and those that 

 are enabled to climb by means of some substance which 

 they have the power of secreting. 



The first order of climbers — those that climb by means of 

 their claws — includes a large proportion of insects, especially 

 in the Coleoptera order — the majority of those that have five 

 joints in their tarsi being of this description. The predaceous 

 tribes, particularly the numerous and prowling ground-beetles 



1 De Geer, vii. 38. t. iii. f. 10. rr. 



2 This insect abounds at East Farleigh, near Maidstone. 



