80 INTRODUCTION. 



still comparatively unknown, authors had agreed to 

 terminate the mammals by cetacea, because these 

 approached the class of fishes as just mentioned. 

 But there being extant, along with true mammalia, 

 that second series, small indeed, and almost isolated 

 in Australia, known by the name of marsupial or 

 pouched animals ; a series organised, in many re- 

 spects, upon a different typical plan, and lower in 

 the scale of nature, but with dentitions and aptitudes 

 running parallel to several orders of true mammals ; 

 and a still smaller group, which, though quadruped 

 and warm blooded, is monotremous, and in many re- 

 spects organised like reptiles ; it followed, that when 

 duly investigated in a natural system, this series 

 could no longer find a proper place between families 

 of true mammalia, but required to be located at the 

 termination of the set of links, which led from man 

 downwards to that order, and was possessed of fa- 

 milies most naturally connecting itself with them. 



We now beg to proceed with a few preliminary 

 observations by way of introduction. 



THE MAMMALIA. 



THE mammalia, that is, all animals that are pro- 

 vided with organs to suckle their young, are placed 

 at the head of the vertebrated series in the animal 

 kingdom. For, even excluding man, we find among 

 them the greatest number of faculties, the most de- 

 licate sensations, the most varied action, and an 

 aggregate of properties for the production of intelli- 



