CLASSIFICATION OF ANIMALS. 9 



anticipate the illustrations of which the present course of lectures 

 will mainly consist. 



Not only the soundest and widest physiological generalisations, but 

 those inductions which, from sometimes being based on a mere 

 fragment of a bone, seem like a divination of the nature and affinities 

 of an extinct species, depend entirely upon a knowledge of the laws 

 of correlation of organic structures, and can only be made by the 

 comparative anatomist, who has studied not only the gradations of 

 structure, but the general combinations of organs which characterise 

 the species of each particular class. 



With these explanations of the grounds which have lead me to 

 change the order in which I propose to bring before you the facts of 

 Comparative Anatomy, I proceed to the proper business of the 

 present course, which must commence by the definitions of the 

 primary groups of animals whose general plan of organisation it is 

 proposed to describe and compare. 



Little useful progress can be made in Comparative Anatomy 

 without some knowledge of Zoology. Zoology is the key to the 

 nature and habits of the animals of which Zootomy unfolds the 

 structure. Some knowledge of natural history and of the principles 

 of classification, therefore, is essential to the comprehension of the con- 

 nection between structure and habits, on which the utility of Com- 

 parative Anatomy in the advancement of Physiology mainly depends. 



The classification of animals is not now what it was in the time of 

 Linnaeus. I do not mean merely to say that animals are differently 

 arranged, but the object and principles of that arrangement are very 

 different. 



Linnaeus in his Systema Naturce wished to give, as it were, a 

 Dictionary of the Animal Kingdom, by reference to which you might 

 as readily ascertain the place of the animal in his system as that of a 

 word in a lexicon, by merely knowing its first and second letters. 

 To this end, Linnaeus selected a few of the most obvious characters 

 for the establishment of his groups. 



Taking, for example, a certain number of incisor teeth, and the 

 pectoral position of the mammae, as the characters of his first order of 

 animals, he thereby associated man with the monkeys and the bats. 

 But, independently of the psychical endowments which place the 

 human species far above the lower creation, it may readily be 

 conceived that great differences of organisation must exist in animals 

 which enjoy the erect position on two feet, in those which climb by 

 having four hands, and in those which fly by virtue of a metamor- 

 phosis of tlieir anterior members into wings. 



External and arbitrary characters, selected merely for the con- 



