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 be 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 sea.s ; 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 

 40 and 50, it may be several degrees higher. Frogs and 

 other aquatic Reptiles 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 1 ; 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 



