PROGRESS OF SYSTEMATIC ZOOLOGY. 417 



riviparous have not all liair ; those which are oviparous have scales.' 

 We have here a manifestly intentional subordination of characters : 

 and a kind of regret that we have not names for the classes here indi- 

 cated ; such, for instance, as viviparous quadrupeds having hair. But 

 he follows the subject into further detail. " Of the class of viviparous 

 quadrupeds," he continues, " there are many genera, 11 but these again 

 are without names, except specific names, such as man, lion, stay, horse, 

 dog, and the like. Yet there is a genus of animals that have names, as 

 the horse, the ass, the oreus, the glnnus, the innus, and the animal 

 which in Syria is called heminus (mule) ; for these are called mules, from 

 their resemblance only ; not being mules, for they breed of their own 

 kind. Wherefore," he adds, that is, because we do not possess recog- 

 nized genera and generic names of this kind, " we must take the species 

 separately, and study the nature of each." 



These passages afford us sufficient ground for placing Aristotle at 

 the head of those naturalists to whom the first views of the necessity 

 of a zoological system are due. It was, however, very long before any 

 worthy successor appeared, for no additional step was made till modern 

 times. When Natural History again came to be studied in Nature, 

 the business of Classification, as we have seen, forced itself upon men's 

 attention, and was pursued with interest in animals, as in plants. The 

 steps of its advance were similar in the two cases ; by successive 

 naturalists, various systems of artificial marks were selected with a view 

 to precision and convenience ; and these artificial systems assumed 

 the existence of certain natural groups, and of a natural system to 

 which they gradually tended. But there was this difference between 

 botany and zoology : the reference to physiological principles, which, 

 as we have remarked, influenced the natural systems of vegetables in a 

 latent and obscure manner, botanists being guided by its light, but 

 hardly aware that they were so, affected the study of systematic zoology 

 more directly and evidently. For men can neither overlook the gene- 

 ral physiological features of animals, nor avoid being swayed by them 

 in their judgments of the affinities of different species. Thus the 

 classifications of zoology tended more and more to a union with com- 

 parative anatomy, as the science was more and more improved. 12 But 

 comparative anatomy belongs to the subject of the next Book ; and 

 anything it may be proper to say respecting its influence upon zoolo- 

 gical arrangements, will properly find a place there. 



:s Cuvier, Ler. d'Anat. Comp. TO! i. p. 17. 

 VOL. II. 27. 



