. SENSE OF TOUCH. 15 



bat is guided wholly by the impression of the air on 

 its wings : and yet we have observed bats, confined 

 in a house, beat themselves against the windows, as 

 wild birds and bees will do, though never against the 

 walls*. Man has the same means of knowledge in a 

 slight degree : for it is easy in the dark to say when 

 one approaches a wall, by the impression of the air 

 on the face. The faculty in the bat of perceiving, 

 and being able to avoid such obstructions, is a pro- 

 vision of creative wisdom well worthy of our notice, 

 as the creature, always flying in the twilight and in 

 the night, could not well depend on its eyes in avoid- 

 ing objects during its rapid flight in pursuit of noc- 

 turnal moths. Moths, and most night-flying insects, 

 possess this faculty in an inferior degree. Beetles, 

 indeed, seem to be deficient either in the power of 

 perceiving objects or of avoiding them, as they often, 

 during the twilight, dash against the traveller, (from 

 which originated the proverb of "blind as a beetle"); 

 but we have never observed any of the night moths 

 thus deceived. 



The feeling of the various degrees of temperature, 

 whether hot or cold, is so different from the other per- 

 ceptions of touch, that some naturalists, among whom 

 are Darwin and Fleming, refer it to a peculiar sense. 

 As insects appear to be extremely susceptible of 

 varying temperature, we must not pass it over with- 

 out notice. Dr. Fleming distinguishes what he terms 

 the sense of heat from touch by its not requiring, like 

 the latter, any muscular effort for its exercise f. That 

 there are peculiar nerves in various parts of the skin 

 appropriated to the perception of heat, Dr. Darwin 

 thinks is proved by the heat of a furnace giving no 

 pain to the nerve of the eye, while it scorches and 

 pains the parts adjacent. Warm water, again, or warm 

 * J. R. f Philosophy of Zoology, i. 171. 



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