320 THE MECHANICAL FUNCTIONS. 



Insects of the Sphinx tribe are also provided with 

 a kind of rudder formed by the expansion of the 

 tail, enabling them to steer their course with more 

 certainty. The Lepidoptera in general fly with the 

 body nearly upright, contrary to the habits of most 

 other winged insects, whose bodies, while flying, 

 are nearly in a horizontal position. 



The feats of agility and strength exhibited by 

 insects have often been the theme of admiration 

 with writers on natural history ; and have been 

 considered as affording incontrovertible proofs of 

 the enormous power with which their muscles must 

 be endowed. We have already had occasion to 

 notice a remarkable instance of the force and per- 

 manence of muscular contraction in those cater- 

 pillars which frequently remain for hours together 

 in a fixed attitude, with their bodies extended'from 

 a twig, to which they cling by their hind feet 

 alone.* Ants will carry loads which are forty or 

 fifty times heavier than their own bodies ; and the 

 distances to which many species, such as the 

 Tlallica, the Locust, the Lepisma, and above all 

 the Pulecv, are capable of leaping, compared with 

 the size of the insects themselves, appear still more 

 astonishing. Linnaeus has computed that the 3Ie- 

 lolontha, or chaffer, is, in proportion to its bulk, 



and Esprit Gioina, Trans. Linnean Soc. i. 135. The same object 

 is effected in the Iclmeiimon, (which belongs to the order Hymen- 

 optera,) by the catching of the nervure, which forms the posterior 

 margin of the upper wing, into a series of hooks projecting from the 

 anterior margin of the lower wing. De Geer counted more than forty 

 of these hooks on each of the lower wings of a large ichneumon. 

 Ibid. i. 562. Mr. Ashton has discovered that the wings of the 

 Homoptera are locked together in a similar manner. 

 * See Fig. 148*, p. 281. 



