PARTS OF INSECTS, AND MISCELLANEOUS OBJECTS. 



129 



A triple claw of a spider is exhibited in figure 218 ; the several hooks are not 

 smooth, but are armed with 



teeth 0*1 one side, and pre- Flg - 218p 



sent quite a formidable ap- 

 pearance. The length of 

 the tooth, a, the third from 

 the end, on the middle hook, 

 is the five hundredth part 

 of an inch. 



By the aid of their claws, 

 insects are enabled to move 

 over rough substances with 

 great facility, either up- 

 ward or downward, but 

 upon polished surfaces they 

 advance with the utmost 

 difficulty. Upon the fore- 

 most pair of their feet these 

 hooks are bent backward, 

 on the posterior pair for- 

 ward, and on the third or 

 middle pair, inward ; thus rendering the position of the insect exceedingly sta- 

 ble, and effectually securing it from displacement. The claws are, therefore, 

 highly useful to the insect, either in a state of rest or activity. On the feet of 

 the larger kinds of insects, cushions, composed of thick tufts of fine hair, are 

 found, which prevent it from receiving injury upon leaping from a considerable 

 height. Moreover, these delicate and elastic hairs adapting themselves to the 

 asperities on the bodies which the insects frequent, enable the latter to adhere to 

 them with much tenacity. But a more efficient apparatus is possessed by some 

 of these little creatures, which gives them the power of walking in any position 

 upon smooth and glassy surfaces. It consists of suckers, so adapted to the foot, 

 that the insect is sustained by the pressure of the air upon the sucker. 



The sucker consists of a thin membrane, capable of expansion and contrac- 

 tion, having the edges serrated or notched, so that it can be made to fit closely 

 to surfaces of every shape. The sucker acts in precisely the same manner as 

 the circle of leather with a string attached to the centre, which lads use in their 

 sports to take up stones and pebbles, the leather being first wetted in order to 

 make it adhere closely to the stone. The common house-fly has two suckers to 

 each foot, immediately under the root of the claw, and attached by a narrow 

 neck capable of motion in all directions. These appendages are delineated in 

 figure 219, which represents the suckers on the under side of the foot of a blue- 

 bottle fly, with the claws of the insect branching over them. In the horse-fly, 

 every foot is provided with three suckers ; and in the yellow s?w-6y, four are 

 arranged along the under surface of the toes, one upon each of the four first 

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