2 ON CLASSIFICATION. 



the 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 red cold 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 inverte- 

 brate animals, to which latter he gives the general name of vermes, 

 worms. 



We shall not in this place comment upon the want of anatomi- 

 cal knowledge conspicuous in the above definitions, or the insuffi- 

 cient data afforded by them for the purposes of Zoology. The appa- 

 ratus of circulation, being a system of secondary importance in the 

 animal economy, was soon found to be too variable in its arrange- 

 ment 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 ob- 

 tained 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 im- 

 portance of each, and sketching out with a master hand the 

 outlines of that arrangement since adopted as the most natural 

 and satisfactory. ( 



The result of the labours of this illustrious man cannot but 

 be of dee*p 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 



* Systema Naturae Vindobonae, 1767. Thirteenth 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. Fart I. 1835. 



