CLASSIFICATION BY SERIES. 



477 



cognising 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 included in it 

 which exhibits the properties consti- 

 tutive of the class in the highest de- 

 gree, conceiving the other varieties as 

 instances of degeneracy, as it were, 

 from that type, deviations from it by 

 inferior intensity of the characteris- 

 tic property or properties. For every 

 phenomenon is best studied {ccBtei'is 

 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 fvilly known to us, so 

 that we may learn to recognise their 

 small degrees, or even their mere rudi- 

 ments, 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 de- 

 grees 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 pro- 

 perties may nevertheless be of great 

 avail towards the discovery of the con- 

 ditions and laws of the general pheno- 



menon of life, which is common to man 

 with those inferior animals. And 

 they are, even, rightly considered as 

 properties of animated nature itself ; 

 because they may evidently be affili- 

 ated to the general laws of animated 

 nature ; because we may fairly pre- 

 sume that some rudiments or feebl6 

 degrees of those properties would be 

 recognised in all animals by more per- 

 fect organs, or even by more perfect 

 instruments, than ours ; and because 

 those may be correctly termed pro- 

 perties of a class which a thing exhi- 

 bits exactly in proportion as it belongs 

 to the class, that is, in proportion as it 

 possesses the main attributes consti- 

 tutive of the class. 



§ 4. It remains to consider how the 

 internal distribution of the series may 

 most properly take place : in what 

 manner it should be divided into 

 Orders, Families, and Genera. 



The main principle of division must 

 of course be natural affinity ; the 

 classes formed must be natural groups; 

 and the formation of these has already 

 been sufficiently treated of. But the 

 principles of natural grouping must be 

 applied in subordination to the prin« 

 ciple of a natural series. The groups 

 must not be so constituted as to place 

 in the same group things which ought 

 to occupy different points of the gen- 

 eral scale. The precaution necessary 

 to be observed for this purpose is, 

 that the fHmary divisions must be 

 grounded not on all distinctions indis- 

 criminately, but on those which cor- 

 respond to variations in the degree of 

 the main phenomenon. The series of 

 Animated Nature should be broken 

 into parts at the points where the 

 variation in the degree of intensity of 

 the main phenomenon (as marked by 

 its principal characters, Sensation, 

 Thought, Voluntary Motion, &c.) 

 begins to be attended by conspicuous 

 changes in the miscellaneous proper- 

 ties of the animal. Such well-marked 

 changes take place, for example, where 

 the class Mammalia ends ; at the 

 points where Fishes are separated 



