70 



PETTIGREW ON THE MECHANISM OF FLIGHT. 



poster 



tating or twisting in 



Tliis is better seen in fig. 25. "When the 



are reversed; the anterior thick margins ro- 



osterior thin ones in a downward direction. 



Here, again, the wings are jointed in such a manner as to ensure tneir aescnomg a spiral course. 

 ['he Locust (Gry litis migratorius) . In the Locust the upper (r) and under (/) wings are semimem- 

 branous and independent of each other. The under wings {a, b) during repose are crushed up after 

 tin* manner of a fan. In flight they are expanded and rotated or twisted as in the Beetle, Cock- 



roach, and Cicada. Tl 



and act mechanically 



glirici 



Fig. 24- The Dri jonfly {Petalura gigamtea). In this insect the wings are finely curved and delicately 



nr 



anterior margins. 



The anterior pair (e) are analogous in every respect to the posterior (/). 

 Uoth make a certain angle with the horizon, the anterior pair (e), which are principally used as 



(/) 



The wings 



of the Dragonfly make the proper angle for flight even in repose, so that the insect can take to 

 wing instantly. It flies with astonishing velocity. 



I 



■* 



l >:>. 



thick margin (ef) 



the thin one (a b) upwards. The wings 

 slates a house. 



i 



oof 



Fig. 26. The Butterfly IMorpha Helenor, Vampa), from Milne-Edwards. In the Butterfly the wings 



be 



reqi re to be lowered and slewed round until thev make an angle of somethin 



.0 



with the horizon. The wings of the Butterfly rotate on their axes during flight, as in the other 



ins 



with 



comparatively very large wings (a a). The nervures are seen to great ad- 

 vantage in this specimen; and the enormous expanse of the pinions readily explains the irre- 

 gular flight of the insect, on the principle of recoil. 



Plate XIV. 



Fig. 28. The Lammer-Geyer {Gypartos) (from Milne-Edwards), shows powerful deeply concave wings 



'/; 



!• 



wing- fully extended (cb,d'e'f) 



fjcb). In the extended wing 



the 



margin (d'Jf) of the pinion is directed upwards and backwards (vide arrow), the posterio: 

 thin margin (cb) downwards and forwards. The reverse of this happens during flexion, 



anterior or thick margin (def) of the pinion being directed downwards and forwards (vide 



arrow) the posterior or thin margin hearing the rowing-feathers upwards and backwards. The 



ax ^ **"*"ig cALcusiun ana nexion ; ana xnis » <* jr*~- 



ot the utmost importance in the action of the wings, as it enables the bird to rotate the primary, 

 secondary, and tertiary feathers on and off the wind, and to present at one time (in extension) a 



resisting one. 



com 



wings are ample as compared with the 



hunting. In this case the 



wing 



wards. 



antmor or rtnek margins (rf ef) are directed upward,, their posterior or thin margins (e b) dow- 



.»», • r ?E ?' SeqUently makc « ■* of something like 30° with the horizon. The 

 an le . s d.mnnshed dnnng flexion, and ean he altered at the .ill of the bird. It is occasioned 

 !>> the rotatuon of the hones of the ™ g on their axes d„ri, 









