DR PETTIGREW ON THE PHYSIOLOGY OF WINGS. 



425 



This wing, as the figure indicates, is composed of numerous narrow segments 

 iff/, g g g), so arranged that the air, when the wing is made to vibrate, opens 

 or separates them at the beginning of the up stroke, and closes or brings them 

 together at the beginning of the down stroke. 



The time and power required for opening and closing the segments is com- 

 paratively trifling, owing to their extreme narrowness and extreme lightness. 

 The space, moreover, through which they pass in performing their valvular 



Fig. 65. t 



action is exceedingly small. The wing under observation is flexible and elastic 

 throughout, and resembles in its general features the other wings described. 



I have also constructed a wing which is self-acting in another sense. This 

 consisted of two parts — the one part being made of an elastic reed, which 

 tapered towards its extremity, the other of a flexible sail. To the reed, which 

 corresponded to the anterior margin of the wing, delicate tapering reeds were 

 fixed at right angles, the principal and subordinate reeds being arranged on the 

 same plane. The flexible sail was attached to the under surface of the principal 

 reed, and was stiffer at its insertion than towards its free margin. When the 

 wing was made to ascend, the sail, because of the pressure exercised upon its 

 upper surface by the air, assumed a very oblique position, so that the resistance 

 experienced by it during the up stroke was very slight. When, however, 

 the wing descended, the sail instantly flapped in an upward direction, the 



* Fig. 64. x, Ball and socket joint at root of wing, a, b, Anterior margin of wing, c, d, Posterior margin of wing. 

 i, Portion of wing composed of one layer of flexible material, h, Portion of wing composed of two layers, g, Portion 

 of wing composed of three layers. /, Portion of wing composed of four layers, e, Portion of wing composed of five 

 layers. 



+ Fig. 65. Flexible valvular wing with India-rubber springs attached to its root. 

 _ a, b, Anterior margin of wing, tapering and. elastic, c, d, Posterior margin of wing, elastic. /,/,/, Segments 

 which open during the up stroke and close during the down, after the manner of valves. These, are very narrow, 

 and open and close instantly, g, g, g, The same segments magnified, x, Universal joint, m, Superior elastic band. 

 », Ditto inferior, o, Ditto anterior, p, q, Ditto oblique, r, Ring into which the elastic bands are fixed. 



