SCENE ON THE ESSEQUIBO. 41 



Two peculiarities are discoverable in these noc- 

 turnal creatures, which may well detain us a few 

 minutes to observe. Curious is it to remark by 

 what a variety of means the same effect is fre- 

 quently obtained. The eyes of such carnivorous 

 animals as hunt their prey by night, are admirably 

 adapted for seeing in the dark; they possess a 

 faculty not given to those of other species; they can 

 close the pupil entirely. This faculty depends upon 

 the superior sensibility of the retina, upon its being 

 easily affected, because it is needful for them to 

 descry objects with the smallest degree of light. But 

 no such faculty is obvious in the bat, they owe 

 apparently, the facility with which they pass unhurt, 

 even in the darkest nights, through small apertures, 

 and among thick boughs, to the enlargement of 

 another sense. Spallanzani caught several bats, and 

 having covered their eyes, turned them into a dark 

 room, which opened into a narrow way, from which 

 even the faintest ray of light had been carefully ex- 

 cluded. They flew without striking against the 

 walls, and would often suspend their flight when 

 they came to a place where they could conveniently 

 perch : in the passage, which turned at right angles, 

 they would, though at a considerable distance from 

 the walls, change the direction of their flight with 

 the greatest nicety, when they drew near the angles. 

 They also carefully avoided striking against the 

 branches of trees, which Spallanzani had suspended 

 from the roof, and even flew between strong threads, 

 which hung perpendicularly in like manner; though 

 frequently obliged to contract their wings in order 

 to pass between them. It was naturally inferred 



