CLASSIFICATION BY SERIES. 287 



versal laws of animal life. And the classification of animals 

 best suited to that one purpose, is the most suitable 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 

 recognising 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 recognise this 

 identity, or in other words, 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 in- 

 cluded 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 characteristic property or 

 properties. For every phenomenon is best studied (cceteris 

 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 recognise their smaller degrees, or even their 

 mere rudiments, in cases in which the direct study would 

 have been difficult 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 production 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 animated existence, which the 

 inferior varieties of animals do not show. The knowledge of 

 these properties may nevertheless be of great avail towards 



