510 OPERATIONS SUBSIDIARY TO INDUCTION. 



the discoveiy of the conditions and laws of the general phenomenon 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 affiliated to the general laws of animated nature; be- 

 cause we may fairly presume that some rudiments or feeble degrees of 

 those properties would be recognized in all animals by more perfect or- 

 gans, or even by more pei'fect instruments, than ours ; and because those 

 may be correctly termed properties of a class, which a thing exhibits 

 exactly in proportion as it belongs to the class, that is, in proportion as it 

 possesses the main attributes constitutive 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 al- 

 ready been sufficiently treated of. But the principles of natural grouping 

 must be applied in subordination to the principle 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 general scale. The precau- 

 tion necessary to be observed for this purpose is, that the primary divis- 

 ions must be grounded not on all distinctions indiscriminately, but on 

 those which correspond to variations in the degree of the main phenome- 

 non. The series of Animated Nature should be broken into parts at the 

 points where the variation in the degree of intensity of the main phenome- 

 non (as marked by its principal characters. Sensation, Thought, Voluntary 

 Motion, etc.) begins to be attended by coyspicuous changes in the miscel- 

 laneous properties of the animal. Such well-marked changes take place, 

 for example, where the class Mammalia ends ; at the points where Fishes 

 are separated from Insects, Insects from Mollusca, etc. When so formed, 

 the primary natural groups will compose the series by mere juxtaposition, 

 without redistribution ; each of them corresponding to a definite portion 

 of the scale. In like manner each family should, if possible, be so subdi- 

 vided, that one portion of it shall stand higher and the other lower, though 

 of course contiguous, in the general scale ; and only when this is impossi- 

 ble is it allowable to ground the remaining subdivisions on characters hav- 

 ing no determinable connection with the main phenomenon. 



Where the principal phenomenon so far transcends in importance all 

 other properties on which a classification could be grounded, as it does in 

 the case of animated existence, any considerable deviation from the rule 

 last laid down is in general sufficiently guarded against by the first princi- 

 ple of a natural arrangement, that of forming the groups according to the 

 most important characters. All attempts at a scientific classification of 

 animals, since first their anatomy and physiology were successfully studied, 

 have been framed with a certain degree of instinctive reference to a natu- 

 ral series, and have accorded in many more points than they have differed, 

 with the classification which would most naturally have been grounded on 

 such a series. But the accordance has not always been complete; and it 

 still is often a matter of discussion, which of several classifications best ac- 

 cords with the true scale of intensity of the main phenomenon. Cuvier, 

 for example, has been justly criticised for having formed his natural 

 groups, with an undue degree of reference to the mode of alimentation, a 

 circumstance directly connected only with organic life, and not leading to 



