88 HIGHLY SPECIALIZED FORM OF FLIGHT 

 stellatarum), yet they are rivalled by insects 

 possessing only a single pair of wings. For 

 instance, there is a dipterous fly (Bombylius) 

 which, in its mode of feeding, poise and flight, 

 exactly resembles stellatarum in miniature, 

 and produces the same humming sound, but 

 in a higher key. 



I am incUned to think that this flight of 

 Bombylius (three British examples), which is 

 identical with that of the humming-birds, 

 some of the hawk-moths and the hover-flies, 

 is a form of flight distinct and more highly 

 specialized than is observed in any other 

 classes, albeit there are some inferior imita- 

 tions. The speciality of this flight lies in the 

 fact, I believe, that the rate of wing vibration 

 is constant, whether the insect, or bird, is 

 stationary, as when poising over a flower, or 

 travelling at excessive speed. 



A hover-fly, for instance, suspended in mid- 

 air, remains absolutely stationary though its 

 wings are vibrating with such velocity as to 

 render them practically invisible. Suddenly 

 the fly darts off so rapidly that the eye can 

 scarce follow, when again it returns to the 

 same spot. Like the flight of thought, a 

 moment here and then away, regardless of 

 time and space. But though the spirit that 

 prompts these ethereal excursions is itself 



