26 ORGANIZATIONOFREPTILES. 



is 98° of Fahrenheit, and in some of the Birds it is even higher than this. Mam- 

 malia and Birds have the power of preserving this temperature during hfe; the 

 heat of the body being maintained by respiration, gives them the abiUty of gene- 

 rating and preserving a uniform temperature under all circumstances, whether in 

 hot or in cold climates. In Reptiles on the contrary, where but a moiety of the 

 blood is carried to the lungs, and this only at irregular intervals, we find their 

 temperature but little removed from that of the medium in which they live. Not 

 having the power of generating the necessary degree of heat to preserve an equable 

 temperature, it follows that cold renders the animal torpid, and even, if too intense, 

 destroys it altogether. The temperature of land Tortoises and Frogs is about 

 40°, when that of the atmosphere is 35° of Fahrenheit. Hunter,* by freezing 

 mixtures, reduced the temperature of the stomach of a Frog to 31°; below this, it 

 could not be diminished without destroying the animal. From these observations, 

 it results that external heat is more necessary to the existence of Reptiles than of 

 all other vertebrated animals; heat increasing their activity, their sensibility, 

 growth, and developement, the largest species being always found in the tropical 

 regions. Cold abstracts their caloric, benumbs their faculties, renders them torpid 

 and inactive; and as winter approaches, they seek a shelter — some, as the Gopher, 

 in holes excavated by itself in the earth, others under the bark of trees, or in the 

 crevices of rocks; many retire to the reedy banks or muddy beds of rivers, and as 

 the degree of cold increases, they fall into a deep sleep, "the twin sister of death," 

 which neither noise nor even wounds can interrupt. At this time the functions 

 of organic life alone are active: the circulation is languid, the respiration suspended 

 — at least pulmonary respiration — for many of them hybernate in mud, covered 

 with water, and in other situations where no atmospheric air can penetrate the 

 lungs. Buried in this profomid sleep, they remain until the returning heat of spring 

 restores them to life and activity. In Carolina, where the winters are seldom 

 severe, the hybernation is never complete; a few warm days in the winter restore 

 them to life; I have often met the Rana gryllus and various Water-snakes, in 

 January, and have seen the Scaphiopus, attended by its mate, in very warm 



* Observations on the Animal Economy, p. 104. 



