418 DR PETTIGREW ON THE PHYSIOLOGY OF WINGS. 



tion to this theory — the bats and birds, and some, if not all, the insects have 

 distinct elevator muscles. The presence of well-developed elevator muscles 

 implies an elevating function ; and, besides, we know that the insect, bat, and 

 bird can elevate their wings when they are not flying, and when, consequently, 

 no reaction of the air is induced (pages 364, 365, 395, 396, and 397). 



Straus-Durckheim's Views. — Durckheim believes that the insect abstracts 

 from the air by means of the inclined plane a component force (composant) 

 which it employs to support and direct itself. In his Theology of Nature he 

 describes a schematic wing as follows : — It consists of a rigid ribbing in front, 

 and a flexible sail behind. A membrane so constructed will, according to him, 

 be fit for flight. It will suffice if such a sail elevates and lowers itself successively. 

 It will, of its own accord, dispose itself as an inclined plane, and receiving 

 obliquely the reaction of the air, it transfers into tractile force a part of the 

 vertical impulsion it has received. These two parts of the wing are moreover 

 equally indispensable to each other. If we compare the schematic wing of 

 Durckheim with that of Borelli they will be found to be identical, both as 

 regards their construction and the manner of their application. 



Marey's Vieivs continued. — Professor Marey, so late as 1869, repeats 

 Borelli's arguments and views with very trifling alterations. Marey describes 

 two artificial wings, the one composed of a rigid rod and sail — the rod repre- 

 senting the stiff anterior margin of the wing; the sail, which is made of paper 

 bordered with card board, the flexible posterior portion. The other wing 

 consists of a rigid nervure in front and behind of thin parchment which sup- 

 ports fine rods of steel. He states, that if the wing only elevates and depresses 

 itself, " the resistance of the air is sufficient to produce all the other move- 

 ments. In effect the wing of an insect has not the power of equal resistance 

 in every part. On the anterior margin the extended nervures make it rigid, 

 while behind it is fine and flexible. During the vigorous depression of the 

 wing the nervure has the power of remaining rigid, whereas the flexible 

 portion, being pushed in an upward direction on account of the resistance it 

 experiences from the air, assumes an oblique position which causes the upper 

 surface of the wing to look forwards." The reverse of this takes place during 

 the elevation of the wing — the resistance of the air from above causing the 

 upper surface of the wing to look backwards. . . . "At first the plane of 

 the wing is parallel with the body of the animal. It lowers itself — the front 

 part of the wing strongly resists, the sail which follows it being flexible yields. 

 Carried by the ribbing (the anterior margin of the wing) which lowers itself, the 

 sail or posterior margin of the wing being raised meanwhile by the air, which sets 

 it straight again, the sail will take an intermediate position, and incline itself 

 about 45° plus or minus according to circumstances." 



" The wing continues its movements of depression inclined to the horizon, but 



