DR. PETTIGREW ON THE MECHANISM OF FLIGHT 



manner that the membranous wings can be folded (e) transv 



durin 



«rs are directed 



outwards and slightly downwards, the posterior or thin margins inwards and slightly upwards 

 During extension the positions of the margins are reversed by the wingi twisting and rotating 

 upon their axes, the anterior margins, as in bats and birds, being directed upwards, and making 

 a very decided angle with the horizon. The wings in the beetles are insi nitieantly mull when 

 compared with the area of the body. They are, moreover, finely twisted upon ihcu^Ucs, and 

 possess great power as propellers and elevators. 



Under 



that the nervures {d,e,f,n,n,n) are arranged, along the anterior mMgins of the wingi and 

 throughout their substance generally, very much as the bones of the arm (fig. I5r), fo.varn 



(/) 



(d) 



i is 



mode 



The wing is folded npon itself at the point e during rcpM 



Flying 



lilioih 



(a b) is more 



neck, back, and tail, and by the anterior and posterior extremities. The Flying Congo take 



leaps; and the amount of surface which it displays all but enables it to fly. Im 

 cured in the bat, Phvllorhma gracilis (fig. 15), with a very slight increase of surface, 



enormous 



membranous 



The surfaee 



the greatly elongated phalanges taking a principal part. 

 exceeds, as has been explained, that displayed by many insects (compare with figures 10, 1, 

 and 19) and birds (compare with figures 31, 32, and 31, Plate XIV.). The wing, o he bat 

 are deeply concave, and so resemble the wings of beetles ^^^^^f ( ^ 

 winged birds (fig. 32, Plate XIV.). 



(d 



winged Dims ing. o£, rime ax*.;. -*-"~ — V , c 4.1 .;«« «tw1 



of the bat (fig! i, support toe anterior or thick margin •-"-•£-* • ' ' «* £ 



nervnres 



/ 



Fig. 19. SpUnVMot; h^laiW body and comparatively small wings. The *p ,-£- t 



curved and twisted npon themselves, and aet as heliees or screws durmg ftgt - P" 

 great elevating- and driving-powe, If this moth be compared w.,1, the Butt, „■ - . 



Lill at once be perceived that no fixed relation can exist as to the wcght o. the body 



Wl 



(M 



moulded 



The Blnebottle flies with great rapidity, pre, -on, and po„cr. 



The 



wings are not unlike those of the moth (fig. 19). wing-ewer, (r) are semimem- 



Fig. 21. The Cockroach {Tetrachjta porosa). ■ In tins mseet the cH t, . or u ^ ^ 



branous , they are geared to ^membranous or m, or wmg ^ ^ ^ 



gether in flight. When so geared, the upper and unto un ^ ^ ^ - 



and finely graduated from within outwards and [bm bcfoi o ^ ^ . ? ^^^ 



manner 



liereas 



The - une 



the anterior or thick margins of the upper ana una* » ^ ^ , 



when the wings are extended, as shown in the figure, tnej cxte won 



certain angle with the horizon. This change . oeca,oned by t. 



describing a spira! course which causes thorn ^ to J> ^ 



happens in the bat and K-l the conformation of the joints in 



movement in question. 



Pig. 22. The Cicada, as seen from above dm 



- « , ■ 



In this 



margins of the wings {ef) 



VOL. XXVI. 



•J 



