INSKCTA. 24-3 



of securely holding the female during sexual union, than as being 

 specially connected with locomotion. 



In the anterior legs of the male Dytiscus the three first joints of 

 the tarsus are excessively dilated, so as to form a broad circular 

 palette : on examining the inferior surface of this expanded portion 

 under a microscope, it is seen to be covered with an immense num- 

 ber of sucking-cups (Jig. 107, F), two or three being much larger 

 than the rest, but they form collectively a wonderful instrument of 

 adhesion. 



The middle pair of legs of the same beetle (Jig. 107, A) exhibit 

 a somewhat similar structure ; but, in this case, the disc upon which 

 the sucking apparatus is placed is much elongated, and the suckers 

 are all of small dimensions. 



In the female Dytiscus (Jig* 109, c) this configuration of the 

 tarsus is wanting, and, moreover, the surface of the back is marked 

 with deep longitudinal grooves that do not exist in the male insect, 

 but seem to be an additional provision for facilitating the inter- 

 course of the sexes in these powerful aquatic beetles. 



(284.) Another mode of progression common among insects is 

 by leaping, to which, from their extraordinary muscular power, these 

 little beings are admirably adapted. The common flea, for example, 

 (Pulex irritansy) (Jig. 110), will leap two hundred times its own 

 length ; and many Orthoptera possess a power of vaulting through 

 the air scarcely less wonderful, of which the cricket affords a fami- 

 liar instance. In such insects (Jig. 102, A, B) the thighs of the 

 posterior legs are enormously dilated, and the length of these 

 limbs is much greater than that of the anterior pair. When dis- 

 posed to leap, such insects bend each hind-leg, so as to bring the 

 tibia into close contact with the thigh, which has often a longitudi- 

 nal furrow armed on each side with a row of spines, to receive it. 

 The leg being thus bent, they suddenly unbend it with a jerk, 

 when, pushing against the plane of position, they spring into the 

 air.* In many of these saltatorial tribes the tarsus is furnished 

 with very curious appendages, either provided for the purpose 

 of taking off the jar when the animal alights from its lofty 

 leaps,')" or else by their elasticity they may act like firm cushions, 

 adapted to give greater effect to the spring which raises the insect 

 from the ground. In the magnified view of the tarsus of an Abys- 



* Kirby and Spence, Introduction to Entomology, 4 vols. 8vo. 

 t Sir E. Home, Phil. Transact. 1816. 



