CHAPTER XL 



THE PRINCIPLES OF NATURAL HISTORY CLASSIFICA- 

 TIONS. 



ILLUSTRATED BY A STUDY OF THE CLASSIFICATION OF THE ANIMAL 



KINGDOM. 



FOR a clear understanding of the meaning ot the origin of 

 species it is essential to consider the nature of the nomenclature 

 of the classification of organisms We have already consid- 

 ered what species are and what the organic individual is, and 

 how development is an appropriate term for the growth and 

 perfection of the individual, and how evolution pertains to the 

 progressive modifications of the successive species of a genus. 



Classifications in Natural History. Classifications and sys- 

 tems of classification in natural history are but methods of 

 expressing, briefly, almost symbolically, the knowledge we 

 already possess of the characters of organisms and their rela- 

 tions to each other. A single word, the name of a class or 

 order, or even the specific name of a species, stands for all the 

 morphological and physiological characters peculiar to that 

 species, order, or class. Hence such terms are highly tech- 

 nical : and though it may not be possible to learn the full 

 meaning of any of them in a brief course of lectures, it will 

 be possible to describe the right manner of using them, so 

 that the knowledge of the details will be arranged in an or- 

 derly manner under the proper heads as it is gradually ac- 

 quired. 



Species and Genus of Aristotle. As the facts of biological 

 science have accumulated it has been found necessary to dis- 

 tribute them in some systematic manner, and for this purpose 

 a number of arbitrary divisions having definite names has 

 been gradually evolved. The use and meaning of these names 

 will be most easily explained by a brief examination of their 

 development from the terms Species and Genus of Aristotelian 



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