422 



MOTION. 



of the under wing 0.65 ; the sum of the areas 

 of the two wings consequently is =1.25 ; but 

 when placed in the position of flight, as the 

 anterior wing lies partially over the under wing, 

 the whole effective surface of the two wings 

 measures 0.83, and that of the four 1.66 iu. 

 During repose the dorsal planes of the wings 

 of the diurnal Lepidoptera are directed verti- 

 cally and brought into contact. 



Nocturnal Lepidoptera. Many of this order 

 have large organs of flight ; their wings, which 

 in repose lie in or beneath the horizontal plane, 

 are triangular, their apices being the most dis- 

 tant points from the body when the wings are 



extended, and their areas are in the inverse ratio 

 of their velocities, and their distances from the 

 centre of gravity. Thus in the Erebus Strix (Jig. 

 221) the wings are greatly expanded and of a form 

 the best calculated for rapid flight, the areas 

 of the sections of the wing being, for the most 

 part, in the inverse ratio of their distances from 

 the axis of motion; consequently the reverse 

 of that of the Pontia, the Morpho, and most 

 of the diurnal Lepidoptera. The anterior wing 

 is much larger than the posterior, being as 

 7.175 to 5.095 square inches. The area of the 

 four wings is therefore about 12.270 inches, 

 which, being very considerable in proportion 



Fig. 221. 



o 



.0 



