250 THE CANADIAN NATURALIST. [-^"g« 



of structure. Animals tlius constructed on similar plans are said 

 to have an ajinitt/ to each other. 



It is evident that this consideration of homology or affinity, if 

 we can really detect it in nature, should be a primary ground in 

 our arrangement; because, if we regard nature as an orderly 

 system, and still more if we regard it as the expression of an 

 intelligent mind, this must be the aspect in which we can best 

 comprehend its scheme or plan of construction. 



As a simple illustration of this and the preceding heads, we may 

 suppose that we are writing a treatise on architecture, or the art 

 of building. We observe 1st, that there are differences of mate- 

 rial employed, as stone, brick, or wood ; 2nd, that there are various 

 grades of buildings, from the simplest hut to the most elaborate pal- 

 ace or temple ; 3rd, we find a great variety of uses for which build- 

 ing are constructed, and to which they are adapted; 4th, there are 

 different orders of architecture or styles, which indicate the 

 various plans of construction adopted. It will, in studying such 

 a subject, be the most logical order to consider, 1st, the several 

 orders of architecture or plans or types adopted ; 2nd, under each 

 of these to classify the various kinds of buildings according to their 

 uses; 3rdly, under each of these secondary heads, to treat of 

 buildings more or less elaborate or complex ; and 4thly, to con- 

 sider the materials of which the structures maybe composed. This 

 is precisely what the most successful formers of systems have done 

 in natural history, in dividing the animal kingdom into provinces 

 or branches, classes, orders, and genera. On the other hand, 

 classifications produced by mere anatomists who content themselves 

 with a close adherence to similarity of structure and rigid defini- 

 tions based on these, may be compared to a system of architec- 

 ture produced by a mere bricklayer, who regards only the mate- 

 rials used and the manner of putting them together. 



4. The General Nature of the Animal. 



Having settled the more important of the general principles of 

 classification, we now proceed to their practical application ; and 

 first, as a necessary preliminary, to ascertain what we understand 

 by the term Animal, and what are the precise limits of the Ani- 

 mal Kingdom. 



In answer to the question. What is an animal ? we may say 

 in the first place that the animal is a being possessing organisation 

 based on cell-structures, and vital force. This suffices to distin- 



