334 TEMPERATURE OF FISHES AND REPTILES. 
wise have suffered from cold, into deep waters; and those 
species which are confined to shallow lakes and ponds, and 
which are thus liable to he frozen during the winter, are fre¬ 
quently endowed with sufficient tenacity of life, to enable 
them to recover after a process which is fatal to animals much 
lower in the scale. Fishes are occasionally found imbedded 
in the ice of the Arctic seas; and some of these have been 
known to revive when thawed. 
406. In Reptiles, the power of maintaining an uniform tem¬ 
perature is somewhat greater; being especially shown when 
the external temperature is reduced very low. Thus when 
the air is between 60° and 70°, the body of a Reptile will 
be nearly of the same heat; but when the air is between 
4.0° and 50°, it may be several degrees higher. Frogs and 
other aquatic Keptiles have a remarkable power of sustaining 
a temperature above that of freezing, when the water around 
is not only congealed, but is cooled down far below the 
freezing-point. Thus in ice of 21°, the body of an edible 
frog has been found to be 37^°; and even in ice of 9°, the 
animal has maintained a temperature of 33°. In these cases, 
as in Animalcules, the water in immediate contact with the 
body remains fluid, so long as the animal can generate heat; 
but at last it is congealed, and the body also is completely 
frozen. But it is certain that Frogs, like Fishes, may be 
brought to life again, after the fluids of their bodies have 
been so completely congealed that their limbs become quite 
brittle; it is not known, however, whether this may happen 
with other Reptiles. It would appear that among Reptiles, 
as among Fishes, some of the more active species have the 
power of maintaining their bodies at a temperature consider¬ 
ably higher than that of the atmosphere ; thus in some of the 
more agile of the Lizard tribes, the high temperature of 86° 
has been noticed, when the external air was but 71°. 
407. The only classes of animals in which a constantly 
elevated temperature is kept up, are Birds and Mammals. 
The bodily heat of the former varies from 100° to 112°; the 
first being that of the Gull, the last that of the Swallow. In 
general we find that the temperature is the highest in species 
of rapid and powerful flight; and least in those which inhabit 
the earth. Birds that are- much in the water have a special 
provision for retaining within their bodies the heat which 
