16 GENERAL CLASSIFICATION OP ANIMALS. 



and separates them into various divisions and subdivisions, ac- 

 cording to their degree of similarity, and the points in which 

 their structures correspond. Such a system of arrangement 

 is called a Classification of the Animal Kingdom ; and as an 

 accurate acquaintance with the principles on which it is 

 founded, is of great assistance to the student of natural his- 

 tory, I shall proceed to present a general view of that which 

 is most commonly received at the present day.* 



In surveying the series of animals, from the lowest and 

 most insignificant worm, up to man, the lord of the creation, 

 and examining the structure of their bodies, and the mode in 

 which they are enabled to carry on the functions of life, we 

 observe certain lines of distinction among them, which afford 

 ground for arranging them, in the first place, in two grand 

 divisions. Those of the Jirst grand division are possessed of 

 an internal skeleton, a system of bones covered by the flesh, 

 which serves to give form, support, and strength to their whole 

 fabric, and assist in containing the various internal organs, 

 whose actions keep up the life and vigor of the system. Those 

 of the second are not possessed of any such skeleton, but 

 consist of a collection of organs more or less distinct, with- 

 out any solid basis, and are generally of a soft, yielding tex- 

 ture, though occasionally covered and protected externally 

 by a shell or other hard covering. We observe further, that, 

 in animals of the first kind, the blood is always red; in those 

 of the second kind, it is, with a few exceptions, white. 



In those of the first kind, there is always a bony case, 

 called the cranium, or skull, which contains the brain ; and a 

 number of bones, called vertebrae, connected together, so as 

 to form a long column, usually called the spine, the back- 

 bone, or the vertebral column. This column contains a ca- 

 nal extending its whole length, which receives the spinal 

 nerve or marrow, as it passes out of the skull, and conveys it 

 along the trunk, to be from thence distributed to the various 

 parts of the body. It is, as it were, the main pillar or com- 

 mon support of all the rest of the skeleton ; and hence the 

 animals possessed of it are called VERTEBRAL animals, as this 

 forms the most striking characteristic which is common to 

 them all. 



* This system is principally derived from Cuvier. Its general outlines are, 1 

 believe, almost universally admitted to be the most accurate and philosophic al of 

 any yet proposed. In its details, it has not yet perhaps been so generally received ; 

 but I have nevertheless ventured to follow it principally in this work, since there 

 can be little question of its superiority, or that it will ultimately supersede those of 

 all other naturalists 



