336 



DR PETTIGREW ON THE PHYSIOLOGY OF WINGS. 



of 8 movements made by the pectoral fins and tails of fishes, and from finding that 

 in the beetle, blow-fly, and wasp (anterior wings), the posterior margin and body 

 of the wing were inclined forwards (fig. 1 a) with reference to the head of the 

 insect, at the end of the down stroke, and backwards (fig. 1 b) at the end of the 

 up stroke. 



The Wing Rotates upon its Long Axis. — This at once suggested a rotation of the 

 wing upon its long axis along its anterior margin, or, what is practically the 

 same thing, a folding and plaiting of the posterior or thin yielding margin of 

 the wing around the anterior semi-rigid and comparatively unyielding margin 

 — a certain amount of rotation, or what is equivalent thereto, being necessary 

 to reverse and change the planes of the wing at each stroke. 



The Wing Twists and Untwists during its action. — I further observed that the 

 planes of the wing were not only changed at the end of each stroke, but that the 

 wing at this juncture was twisted upon itself, the outer portion of the posterior 

 margin of the wing at the end of the down or forward stroke being inclined 

 forwards (g of fig. 2), while the inner portion was inclined backwards (r of fig. 2) ; 

 whereas at the termination of the up or backward stroke, the outer portion of 

 the posterior margin was inclined backwards (a of fig. 2), while the inner 

 portion was inclined forwards (s of fig. 2). 



»C4 



The Image produced on the Eye by the Wing in Motion is Concavo-Convex, 

 and Twisted. — I likewise discovered that the blur or impression produced on the 

 eye by the rapidly oscillating wing was tivisted upon itself {fig. lcdh,eg f), and 

 more or less concave above (c d e fig. 1), and convex below (fgh fig. 1), a circum- 

 stance which, while it strongly corroborated the opinion that the wing rotated 

 upon its long axis during its vibration indicated that the twisting and reversal 



