CLASSIFICATION BY SERIES. 509 



the degrees in which they exhibit some fact of which we are seeking the 

 law, is too naturally suggested by the necessities of our inductive opera- 

 tions, to require any lengthened illustration here. But there are cases in 

 which the arrangement required for the special purpose becomes the de- 

 termining principle of the classification of the same objects for general 

 purposes. This will naturally and pi'operly happen, when those laws of the 

 objects which are sought in the special inquiry enact so principal a part in 

 the general character and history of those objects — exercise so much influ- 

 ence in determining all the phenomena of which they are either the agents 

 or the theatre — that all other differences existing among the objects are fit- 

 tingly regarded as mere modifications of the one phenomenon sought ; ef- 

 fects determined by the co-operation of some incidental circumstance with 

 the laws of that phenomenon. Thus in the case of animated beings, the 

 differences between one class of animals and another may reasonably be 

 considered as mere modifications of the general phenomenon, animal life ; 

 modifications arising either from the different degrees in which that phe- 

 nomenon is manifested in different animals, or from the intermixture of the 

 effects of incidental causes peculiar to the nature of each, with the effects 

 produced by the general laws of life; those laws still exercising a predom- 

 inant influence over the result. Such being the case, no other inductive 

 inquiry respecting animals can be successfully carried on, except in sub- 

 ordination to the great inquiry into the universal laws of animal life; and 

 the classification of animals best suited to that one purpose, is the most suit- 

 able to all the other purposes of zoological science. 



§ 3. To establish a classification of this sort, or even to apprehend it 

 when established, requires the power of recognizing the essential similarity 

 of a phenomenon, in its minuter degrees and obscurer forms, with what is 

 called the same phenomenon in the greatest perfection of its development ; 

 that is, of identifying with each other all phenomena which differ only in 

 degree, and in properties which we suppose to be caused by difference of 

 degree. In order to recognize this identity, or, in other Avords, this exact 

 similarity of quality, the assumption of a type-species is indispensable. We 

 must consider as the type of the class, that among the Kinds included in 

 it, which exhibits the properties constitutive of the class, in the highest 

 degree ; conceiving the other varieties as instances of degeneracy, as it 

 were, from that type ; deviations from it by inferior intensity of the char- 

 acteristic property or properties. For every phenomenon is best studied 

 {cmteris paribus) where it exists in the greatest intensity. It is there that 

 the effects which either depend on it, or depend on the same causes with 

 it, will also exist in the greatest degree. It is there, consequently, and only 

 there, that those effects of it, or joint effects with it, can become fully 

 known to us, so that we may learn to recognize their smaller degrees, or 

 even their mere rudiments, in cases in which the direct study would have 

 been difiicult or even impossible. Not to mention that the phenomenon in 

 its higher degrees may be attended by effects or collateral circumstances 

 which in its smaller degrees do not occur at all, requiring for their produc- 

 tion in any sensible amount a greater degree of intensity of the cause than 

 is there met with. In man, for example (the species in which both the 

 phenomenon of animal and that of organic life exist in the highest degree), 

 many subordinate phenomena develop themselves in the course of his ani- 

 mated existence, which the inferior varieties of animals do not show. The 

 knowledge of these properties may nevertheless be of great avail toward 



