lo LECTURE I. 



to keep together such tribes as most evidently re- 

 semble each other. Naturalists have therefore in- 

 vented several systems or distributions of animals; 

 formed, either from the general external appear- 

 ance, or from the structure of the principal in- 

 ternal organs. 



The most ancient division of animals, (exclusive 

 of the slight sketches to be found in some parts of 

 the sacred writings,) is that of Aristotle, who divided 

 animals into viviparous or such as produce living 

 and perfectly-formed young, and into oviparous, or 

 such as produce eggs, from which the young are 

 afterwards excluded. This distinction of animals 

 was not conducted with perfect exactness, and 

 Aristotle himself was sensible that it was liable to 

 some exceptions, and that it contained certain inac- 

 curacies. It continued however to be in use, Avith 

 some modifications, till towards the decline of the 

 seventeenth century, when our famous Mr. Ray 

 formed a new classification of animals, founded 

 chiefly on the structure and nature of the heart 

 and lungs in the different tribes ; and the Linnaean 

 arrangement of the animal kingdom still acknow- 

 ledges that of Ray for its basis ; particularly with 

 respect to quadrupeds. 



