452 HERPETOLOGY. 



forests, and extended pestilential swamps. They are. termed 

 COLD-BLOODED ANIMALS, their natural temperature being not 

 much, if at all, above that of the atmosphere or water in which 

 they dwell. Their power of producing animal heat is very lim- 

 ited, so that the system is at once affected by the lowering of the 

 temperature of the medium which they inhabit. In our climate, 

 and indeed in climates considerably nearer the meridian, they 

 all undergo a state of torpidity, in some sheltered retreat, to 

 which, as a refuge, their instinct directs them, and where they 

 remain during the season of winter. Their blood, though cold, 

 is red. In these, and in fact in all cold-blooded animals, the 

 vital principle is much stronger than in those whose blood is 

 warm. A frog has been kept alive forty days after having been 

 subjected to the total privation of its lungs. The brain, which 

 in reptiles is considerably inferior to that of birds, though supe- 

 rior to that of fishes, is not so essentially requisite to the exer- 

 cise of their animal and vital functions as in the mammalia; for 

 they continue to live and to execute voluntary movements for a 

 considerable time after being deprived of it, and even after the 

 loss of the head ; their muscles also are strong and preserve 

 their irritability for some time after life would appear to be ex- 

 tinct; their heart continues to pulsate for hours after it has been 

 torn from the body. In the reptiles this organ is strikingly pecul- 

 iar. In warm-blooded vertebrates it consists of two auricles 

 and two ventricles ; the left ventricle furnishing the system with 

 blood, which, in the capillary vessels of the lungs has been 

 acted on by the external atmosphere. In Reptiles the heart con- 

 sists of but one ventricle and two auricles ; and of these the 

 right auricle receives the vitiated blood returned from the sys- 

 tem to the heart ; the left auricle receives the arterialized blood 

 returned from the lungs ; and both auricles convey their con- 

 tents into the cavity of the ventricle. The vitiated and the arte- 

 rialized blood thus become more or less mixed together ; part 

 of this mixed fluid is sent through the great arterial trunk, as a 

 supply to the system, and part through the pulmonary arteries to 

 be further oxygenated in the lungs, this ventricle having in it- 

 pelf the branching arteries both of the body and the lungs. 

 Such is the circulation in the tortoises, lizards, and snakes. The 

 blood of Reptiles is characterized by the possession of the larg- 

 est globules to be found in the entire sub-kingdom of Vertebrates. 

 Those in the tailed Batrachians, as the Siren, &c., are visible to 

 the naked eye. As in fishes and in birds, these globules are 

 elliptical in their outline, whereas in the Mammals, excepting the 

 Camelida, they are circular. 





