CHAPTER VI. 



DIVISIONS OF THE ANIMAL KINGDOM AND SUCCESSION 

 OF ORGANIC TYPES. 



IT seems hardly necessary to remark that Palaeontology, as 

 a science, is based upon the kindred sciences of Zoology and 

 Botany, and that no satisfactory acquaintance with the former 

 can be arrived at without the previous acquisition of some 

 knowledge of the latter. It cannot be pretended to teach 

 here even the rudiments of these sciences, but there are a 

 few points which may be noticed as having a special bearing 

 upon the study of Palaeontology. 



CLASSIFICATION OF THE ANIMAL KINGDOM. Leaving the 

 vegetable kingdom till we come to speak of fossil plants, a 

 few remarks may be made on the classification of the animal 

 kingdom. Vast as is the number of known animals, all, 

 whether living or extinct, may be classed under some five or 

 six primary divisions or "morphological types," which are 

 technically spoken of as the " sub-kingdoms." All the 

 animals in any one sub-kingdom agree with one another in 

 their structural type, or in the fundamental plan upon which 

 they are constructed ; and they differ from one another 

 simply in the modifications of this common plan. No com- 

 parison, therefore, is possible between an animal belonging 

 to one sub-kingdom, and one belonging to another, since 

 their distinguishing characters are the result of the modifica- 

 tion of two essentially different ground-plans. Hence it is 

 possible to arrange the animals of any one sub-kingdom in 

 something like a linear series, in which the lowest of the 



