254 



MOTIONS OF INSECTS. 



upon it. If it discovered that it was not perfectly opposite, 

 it would immediately slide down again unobserved, and at the 

 next attempt would come directly upon the fly's back. Did 

 the fly happen not to be within a leap, it would move towards 

 it so softly, that its motion seemed not more perceptible than 

 that of the shadow of the gnomon of a dial. If the intended 

 prey moved, the spider would keep pace with it as exactly as 

 if they were actuated by one spirit, moving backwards, for- 

 wards, or on each side without turning. When the fly took wing, 

 and pitched itself behind the huntress, she turned round with 

 the swiftness of thought, and always kept her head towards 

 it, though to all appearance as immovable as one of the nails 

 driven into the wood on which was her station: till at last, 

 being arrived within due distance, swift as lightning she made 

 the fatal leap and secured her prey. 1 I have had an op- 

 portunity of observing very similar proceedings in Salticus 

 scenicus. 



But the legs of insects are not the only organs by which they 

 leap. The numerous species of the elastic beetles (Elater), 

 skip-jacks as some call them, perform this motion by means of 

 a pectoral process or mucro. These animals having very short 

 legs, when laid upon their backs, cannot by their means re- 

 cover a prone position. To supply this seeming defect in their 

 structure, Providence has furnished them with an instrument 

 which, when they are so circumstanced, enables them to spring 

 into the air and recover their standing. If you examine the 

 breast (pectus) of one of these insects, you will observe be- 

 tween the base of the anterior pair of legs a short and rather 

 blunt process, the point of which is towards the anus. Op- 

 posite to this point, and a little before the base of the inter- 

 mediate legs, you will discover in the after-breast (postpectus) 

 a rather deep cavity, in which the point is often sheathed. 

 This simple apparatus is all that the insect wants to effect 

 the above purpose. When laid upon its back, in your hand 

 if you please, it will first bend back, so as to form a very ob- 

 tuse angle with each other, the head and trunk, and abdomen 

 and metathorax, by which motion the mucro is quite liberated 



l Evelyn, quoted in Hooke's Microgr. 200. 



