REPTILIA. 333 



in their breath, and can live in a vacuum a considerable time, in a half 

 state of death. Accordingly nature has made some of this division both 

 terrestrial and aquatic; from which last quality, naturalists have 

 commonly, but improperly, called the whole Amphibia. 



As this class of animals are, as to the construction of the heart, in a 

 kind of middle state between the fish, or dicoilia, and the tetracoilia, it 

 was natural to suppose them to be truly amphibious ; and, while many 

 of them seemed to live both in and out of water, the idea of their being 

 so became still more natural. But although this last circumstance [viz. 

 the heart of three cavities] does not in the smallest degree constitute 

 this property, yet, by those who knew not what it was that did con- 

 stitute an amphibious animal, that alone was deemed sufficient. Some, 

 even, of the Tetracoilia have been termed ' Amphibia,' such as the otter 

 and beaver : but the construction of the heart is not the immediate cause 

 of their being either fish, flesh, or both ; it is whether they have gills, 

 lungs, or both. 



All of this division [or class Tricoilia] sleep in cold weather ; and in 

 their sleep, are as if almost dead. They are, I believe, the only animals 

 that can be called sleepers for seasons ; for we do not find this structure 

 of heart in any other animals, and it is natural to suppose that this 

 property arises from the structure of heart 1 ; and from this structure of 

 heart, and that of the lungs, it would appear that it is not so necessary 

 for the life of these animals to have their blood exposed to the air, as it 

 is in those that are more perfect, and in those that would seem to be 

 less perfect. 



This division of animals may be subdivided into three orders, viz. 

 swimmers, lizards, and snakes. Each order consists of different genera, 

 and those genera into their different species. 



The first order consists of turtles, frogs, toads, efts, and crocodiles. 



The second, of lizards and chameleons. 



The third of snakes. 



[Loose Notes.~\ 

 Amphibia grow slowly, eat little, and breathe slowly. 



As it appears, in general, that Nature can hardly make one part 

 perform two actions with advantage, may we not suppose that the 

 Amphibia see but indifferently, or that they do not see equally well in 

 and out of the water ? 



1 [Bats and insects show that seasonal torpidity may be a property common to 

 animals with very diverse structures of heart.] 



