PERCEPTIONS OP ANIMALS. 401 



the impressions made by external objects on their sentient 

 organs must be of a nature widely difl'erent from those which 

 the same objects communicate to ourselves. While with re- 

 gard to distance and mas2;nitudc our perceptions take the 

 widest range, and appear infinitely extended when com- 

 pared with those of insects, yet they may, in other respects, 

 be greatly inferior. The delicate discrimination of the more 

 subtle affections of matter is, perhaps, compatible only with a 

 minute scale of organization. Thus, the varying degrees of 

 moisture or dryness of the atmosphere, the continual changes 

 in its pressure, the fluctuations in its electrical state, and va- 

 rious other physical conditions, may be objects of distinct 

 perception to these minuteanimals. Organsmayexistinthem, 

 appropriated to receive impressions, of which we can have 

 no idea; and opening avenues to various kinds of knowledge, 

 to which we must ever remain utter strangers. Art, it is 

 true, has supplied us with instruments for discovering and 

 measuring many of the properties of matter, which our un- 

 assisted senses are inadequate to observe. But neither our 

 thermometers, nor our electroscopes, our hygrometers, nor 

 our galvanometers, how^ever skilfully devised or elaborately 

 constructed, can vie in delicacy and perfection with that re- 

 fined apparatus of the senses which nature has bestowed on 

 the minutest insect. There is reason to believe, as Dr. Wol- 

 laston has showm, that the hearing of insects comprehends a 

 range of perceptions very different from that of the same 

 sense in the larger animals; and that a class of vibrations too 

 rapid to excite our auditory nerves, is perfectly audible to 

 them. Sir John Herschel has also very clearly proved that, 

 if we admit the truth of the undulatory theory of lighl, it is 

 easy to conceive how the limits of visible colour may be 

 established; for if there be no nervous fibres in unison with 

 vibrations, more or less frequent than certain limits, such 

 vibrations, though they reach the retina, will produce no 

 sensation. Thus, it is perfectly possible that insects, and 

 other animals, may be incapable of being affected by any of 

 the colours which we perceive; while they may be suscepti- 

 VoL. II. , 51 



