MARCH. 63 



wanting men, however, and among them some names of the 

 highest rank in natural science, who have believed the reports 

 of swallows having been found during winter in holes and 

 caves, or beneath the mud of ponds, in a state of torpidity. 

 But it does not appear that these reports rest on any evidence 

 of sufficient weight to command belief, and they are now 

 generally exploded. 



C. — Is there no heat at all evolved by cold-blooded ani- 

 mals ? or are they always of exactly the same temperature 

 as the surrounding atmosphere ? 



F. — I have some reason to think that a very small 

 quantity of heat is evolved by their circulation ; sufficient to . 

 be quite appreciable by the senses, where many are confined 

 in a small space ; as when a thickly-peopled hive of. bees is 

 about to swarm, the temperature within is considerably above 

 that of the external air : this heat can only be produced by 

 the bees themselves. Another proof is, I think, to be found 

 in the fact, that insects seek crevices and corners to hyber- 

 nate, especially during the pupa state ; this may be partly 

 for concealment, but chiefly I conceive for protection from 

 cold. The same end is probably designed in the silken 

 cocoons of many of those moths which pass the winter in 

 pupa, as silk is a non-conductor of heat. But if their tem- 

 perature were not superior to that of the atmosphere, they 

 would need no protection from non-conducting substances, as 

 the air could abstract no heat from them. 



C. — But if you to,uch a caterpillar or a chrysalis, it seems 

 much colder than the air. 



F. — Our senses are not to be at all depended on, in esti- 

 mating the comparative temperature of different bodies. The 

 feeling cold, or warm, depends on the greater or less power of 

 abstracting heat from our body, and this power depends in 

 a great measure on the smoothness, as well as texture of the 

 abstracting substance. 



