2 INTRODUCTION TO CLASSIFICATION. 



great physiological mechanism, but in relation to one another, 

 to plants and to telluric conditions, would, with equal propriety, 

 dispose of the contents of a Zoological Museum in a totally 

 different manner; basing his classification, not upon organs, but 

 on distributional assemblages. And the pure palaeontologist, 

 looking at life from yet another distinct point of view, would 

 associate animal remains together on neither of these principles, 

 but would group them according to the order of their succession 

 in Time. 



Again, that classification which I propose to discuss in the 

 present pages, is different from all of these : it is meant to 

 subserve the comprehension and recollection of the facts of 

 animal structure ; and, as such, it is based upon purely structural 

 considerations, and may be designated a Morphological Classifi- 

 cation. I shall have to consider animals, not as physiological 

 apparatuses merely ; not as related to other forms of life and to 

 climatal conditions ; not as successive tenants of the earth ; but 

 as fabrics, each of which is built upon a certain plan. 



It is possible and conceivable that every animal should have 

 been constructed upon a plan of its own, having no resemblance 

 whatsoever to the plan of any other animal. For any reason we 

 can discover to the contrary, that combination of natural forces 

 which we term Life might have resulted from, or been mani- 

 fested by, a series of infinitely diverse structures : nor, indeed, 

 would anything in the nature of the case lead us to suspect a 

 community of organization between animals, so different in habit 

 and in appearance, as a porpoise and a gazelle, an eagle and a 

 crocodile, or a butterfly and a lobster. Had animals been thus 

 independently organised, each working out its life by a 

 mechanism peculiar to itself, such a classification as that which is 

 now under contemplation would obviously be impossible ; a 

 morphological, .or structural, classification plainly implying 

 morphological or structural resemblances in the things classified. 



As a matter of fact, however, no such mutual independence 

 of animal forms exists in nature. On the contrary, the different 

 members of the animal kingdom, from the highest to the lowest, 

 are marvellously connected. Every animal has a something 

 in common with all its fellows: much, with many of them; 



