238 DR. PETTIGREW ON THE MECHANISM OF FLIGHT. 



and presenting its maximum of surface, to resume its position of rest and plane of least 



resistance. The principal effort required in flight would therefore seem to be made 



during extension, or when the effective stroke is being given. The elastic ligament is 



variously formed, and the amount of contraction which it undergoes is in all cases 



accurately adapted to the size and form of the wing and the rapidity with which it is 



worked— the contraction being greatest in the short-winged and heavy-bodied insects and 



birds, and least in the light-bodied and ample-winged ones, particularly in such as skim 



or glide. The mechanical action of the elastic ligament, I need scarcely remark, ensures 



an additional period of repose to the wing at each stroke, and this is a point of some 



importance as showing that the lengthened and laborious flights of insects and birds 



are not without their stated intervals of rest. 



Speed attained by Insects.— Many instances might be quoted of the marvellous powers 

 of flight residing in insects as a class. The male of the Silkworm-Moth (Attacus Faphia) 

 is stated to travel more than 100 miles a day* ; and an anonymous writer in Nicholson's 

 Journal t calculates that the common House-fly (Musca domestical & ordinary flight, 

 makes 600 strokes per second, and advances 25 feet, but that the rate of speed, if the° in- 

 sect be alarmed, may be increased six- or sevenfold, so that under certain circumstances it 

 can outstrip the fleetest racehorse. Leeuwenhoek relates a most exciting chase which he 

 once beheld in a menagerie about 100 feet long between a Swallow and a Dragonfly ( Mor- 

 delta). The insect flew with such incredible speed, and wheeled with such address, that 



the Swallow, notwithstanding its utmost efforts, completely failed to overtake and 

 capture it %. 



THE WINGS OF BATS. 



Where the Bat's Wing agrees with and differs from that of the Insect and Bird. 



The wmg of the bat (Plate XV. fig. 66) bears considerable resemblance to that of the 



insect (Plate XV. fig. 65), inasmuch as it consists of a delicate, semitransparent, conti- 



nuous ^brane supported in divers directions, particularly towards its anterior margin 



Plate XV. fig. Wdef), by a system of stays or stretchers («, o,f), which confer upon it 



he degree of ngidity requite for flight. The supports in this instance consist of the 



bones of the arm, forearm, and hand ; and as these fold upon themselves (e) during the 



fbTwt ri^ I C6r , tain ana] ° g r t0 «» — or nervures in the wing of 



the be tie (P ate XV fig. 60 d >e ,f,e,a,o). Indeed, if the wing of the bat and that of some 



Th ™ J.11 \?° m V™^ -U 1» found to possess many features in common. 



They especially resemble each other in their general contour and the manner in which 

 their horny and osseous supports taper from within outward, id * f\ n 1 <■ Z, , 1 

 wards (e, a, b). The wing of the bat van,, T . I '/ } ' fr ° m 1)rfor0 baC 



birds, in some cases being- I£ and £?(££& 7 t "i?* ° f ^ "J 



narrow (Plate XIII. fig. if). It also ^ ^^ «* ">> * oth ™ elo ^ ted ^ 

 ™». ij,„„ ™„,„ JS ' , / ls , oaule . rs as ^ards relative proportion, on some occa- 













being ample with regard to the body, in others comparatively scanty 



It 



* Linn. Trans, vii. p. 40. 



+ 

 + 



t Vol. iii. p. 36. 





;r: H ;^L FaI ! o , n ' J w _ hich " »*■?■»<»«** *. «„. months , hawk 



seizes with the foot and devour, whilst in the air. 1, also k Sw I 1 T t ,f " Dn * mJS ~> ^ ' 













