342 



DR PETTTGREW ON THE PHYSIOLOGY OF WINGS. 



other, the body of the insect being carried along a waved line obliquely upwards 

 and forwards (q r s t, fig. 11, p. 341). The waved track made by the wing is gene- 

 rated by the figure of 8 loops being gradually opened out, these becoming less and 

 less distinct as the insect advances, as is more especially shown at nopqrst of 

 both figures (10 and 11, p. 341). The impulse is communicated to the wing at 

 ac egikmo qsoi fig. 10, and the upward recoil at corresponding letters of fig. 11. 

 The waved track formed by the ascent and descent of the wing of the bat 

 and bird is originated in a similar manner, but in this case the figure of 8 

 loops are disposed more vertically, because of the more vertical direction of 

 the stroke, as shown at efg h ij k I of figure 12. ( Vide also Plate XL figures 

 5 and 6). In this figure (12) the oar, as seen at a b, x s, and cd, represents the 



Fig. 12. 



wing of the bat and bird at the beginning, middle, and termination of the 

 down stroke — the little oar, m n op q r, indicating the cross action of the wing. 

 The large oar is more especially engaged in elevating, the little one in pro- 

 pelling. The manner in which the figure of 8 loops made by the wing of the 

 bat and bird during its ascent and descent are opened out or unravelled by the 



Fiff. 13. 



horizontal travel of the body is shown at a b c d efg h ij klmnop of figure 13 ; 

 the completed waved track being seen at s t u v w of the same figure. 



