EVOLUTION OF LIFE. 59 



left close to their tent, on the surface of the 

 earth ; in less than one hour after it had been 

 killed, at the time that the sky was so serene, 

 that there was not a cloud observable, a small 

 dark spot, at an immense distance in the air, 

 attracted their notice ; this spot gradually in- 

 creased in size, and they soon found that it 

 was a vulture, which was flying in a direct line 

 towards the dead animal, on which it immedi- 

 ately alighted for the purpose of devouring. In 

 less than an hour's time seventy vultures came 

 from all directions, some horizontally, but the 

 major part descended from the upper regions, 

 in which, a few minutes before, no appearance 

 of them was discernible. 



Such, indeed, is the exquisite sensibility of 

 the eye of birds, that they are provided with a 

 membrane, (the membrana nic titans,) which 

 they are enabled to spread over the external 

 surface of it, so as to protect the retina from 

 the injuries which it might sustain, on parti- 

 cular occasions, from the irritation of the solar 

 rays ; and we all know, that the owl, and other 

 birds, are unable to bear the light of day, and 

 that they consequently venture abroad during 

 the night season only. 



The extraordinary faculty which these or- 

 gans of sense possess, is manifested under a 

 multitude of circumstances, which almost chal- 

 lenge our credibility. Carrier pigeons have 



