

DR. PETTIGREW ON THE MECHANISM OF FLIGHT. 277 



marked 



kite 



The upward tendency, however, is checked by the weight of the insect; and its course is mdi- 



marked 



Fig. 73. 



Heron 



•shows the spiral 



>/) 





Tl 



axillary curve pointing downwards; /, posterior axillary curve pointing upwards; 



axillary curve pointing upwards ; b, posterior distal curve pointing downwards. 



axillary and distal curve are reversed in complete extension (compare b a c of the present fig. with 



b a c of fig. 75). 

 Fte. 74. Left wing of Snipe, rather more than half extended, seen from behind. In this figure the poste- 



and distal (6) curves are seen in the act of reversing, the post, rior or thin 



illary 



margin of the wing presenting a straight edge, c b ; def 



wing 



Wild 



margin 



curve 



shows double curve made b\ 

 ision : c a, posterior axillary 



_ . Jtheconvexity of which is directed downwards; ba, posterior distal curve with its 

 convexity directed upwards (compare ca and b a of this figure with b and t of fig. 7S, 

 where the curves are reversed, as in partial flexion) ; def, anterior or thick margin of pinion. 

 When the wing is fully extended, as in the present instance, and the down stroke it made, the 

 air is seized by the concave tip of the wing (/), and passed along the concave under surface of 

 the pinion until it arrives at c, where, the concavity becoming a convexity, the air » permitted 



to escape. ' 

 shown at/cr 



ur 



(tv well 



Fig. 76. Diagram 



g. The fish, in swimming 



d) 



water and letting go or relieving each other alternately. When the tail is delivering the elec- 

 tive stroke, as indicated by the arrowing in the f^^^^S^^ 



fish {d) is reversing, as shown at c. 



These 



track 



Fig. 77. 



Willie tne OOUOie cunc is u«^g «* , — - u„lniwl fnrwmU 



screwing itself forward in two directions, viz. from s.de to side and from bch.n.1 forward, 



screwing iraeu 10 described by the feet of swimmmg-birds. V bra 



Diagram representing the double spira ^^^ , )eforc 1)ackward8> „,, fr „ m ^flu. 

 the right foot (,) is describing the o«ls,<k of V"™^"^" the c ff cctivl . 8trokc , tl , c 



outwards (as represented b y ■« — ^11 J£5— . *- - * right, 

 left foot W is descnbmg the umie of a similar™ n e ( ^ T|ie f| , 



from behind forwards, and from wrthout inwards, in the ion encc 

 thus coordinate each other; and as they reciprocate and abeniate, the double pira! g 



obtained. 

 Diagram : 



the 



arm 



right arm, which likewise advance together. 



2 E 



VOL. XXVI. 



