104 ON ZOOLOGY. 



lead until the time of Linnaeus, who, improving up- 

 on the classifications of both Aristotle and Ray, 

 framed a code of zoology, which, with some mo- 

 difications by Cuvier and Blumenbach, may be 

 considered the prevailing system of the present 

 day. 



Linnaeus first arranged the whole animal king- 

 dom under three grand divisions as derived from 

 the structure of the heart, and the colour and tem- 

 perature of the blood. He next formed animals 

 into six classes, each having reference, not only 

 to the circulating system, but also to some other 

 peculiarity in the animal. Thirdly, into orders 

 according to the structure and functions of a par- 

 ticular external part. Fourthly, into genera, from 

 some general varieties in their conformation ; and 

 lastly into species, from a still greater diversity 

 in their external peculiarities. 



In the first grand division, the animals have a 

 double heart, that is, an organ containing two 

 great cavities, or ventricles, and two smaller ones, 

 or auricles ; and, as the blood of these is of a 

 warmer temperature than the common atmosphere, 

 and is of a red colour, they have been denominat- 

 ed warm, red-blooded animals. They embrace 

 our own species, land quadrupeds, birds, and 

 the whale tribes. 



The animals in the second division, are distin- 

 guished by a single heart, having only one ven- 

 tricle, and one auricle; and in these the blood 



