MARCH. 
63 
wanting men^ however^ and among them some names of the 
highest rank in natural science^ who have beheved 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 ? 
jp. — 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 touch a caterpillar or a chrysalis, it seems 
much colder than the air. 
— 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. 
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