2 ON CLASSIFICATION. 



foundation of his arrangement*, dividing the animal creation into three 

 great sections, characterized as follows : 



I. Animals possessed of warm red blood, and provided with a heart 

 containing four compartments, viz. two auricles and two ventricles. 

 Such are the MAMMALIA and BIRDS. 



II. Animals with cold red blood, their heart consisting of but one 

 auricle and one ventricle, as he believed to be the case in REPTILES and 

 FISHES. 



III. Animals possessed of cold white sanies instead of blood, having 

 a heart consisting of a single cavity, which he designates an auricle : 

 under this head he includes INSECTS and all other invertebrate animals, 

 to which latter he gives the general name of YEEMES, Worms. 



We shall not in this place comment upon the want of anatomical 

 knowledge conspicuous in the above definitions, or the insufficient data 

 afforded by them for the purposes of Zoology. The apparatus of cir- 

 culation, being a system of secondary importance in the animal economy, 

 was soon found to be too variable in its arrangement to warrant its 

 being made the basis of zoological classification, and a more permanent 

 criterion was eagerly sought after to supply its place. 



(4.) Among the most earnest in this search was our distinguished 

 countryman John Hunter, who, not satisfied with the results obtained 

 from the adoption of any one system, seems to have tried all the more 

 vital organs, tabulating the different groups of animals in accordance 

 with the structure of their apparatus of digestion, of their hearts, of 

 their organs of respiration, of their generative organs, and of their 

 nervous system, balancing the relative importance of each, and sketch- 

 ing out with a master hand the outlines of that arrangement since 

 adopted as the most natural and satisfactory f. 



The result of the labours of this illustrious man cannot but be of 

 deep interest to the zoological student, and accordingly an epitome of 

 his ideas upon the present subject is here concisely given. 



The apparatus of digestion appears to be among the least efficient 

 for the purpose of a natural division ; as the separation of animals into 

 such as have a simple digestive cavity, receiving and expelling its 

 contents by the same orifice, and such as have an aperture for the 

 expulsion of the contents of the alimentary canal distinct from that by 

 which food is taken into the stomach, is by no means of practical 

 utility, although this circumstance, as we shall afterwards see, has 

 been much insisted upon. 



Hunter's arrangement of the animal kingdom in conformity with the 

 structure of the heart was a great improvement upon that of Linnccus, 



* Sy sterna Naturce. Vindobonse, 1767. 13th edition. 



t Descriptive and Illustrated Catalogue of the Physiological Series of Comparative 

 Anatomy contained in the Museum of the Royal College of Surgeons in London, 

 vol. iii. parti. 1835. 



