224 ZOOLOGICAL ACCEPTATION OF 



the source of our domesticated animals, of our principal 

 vegetable food, and the ^ "adle of arts and sciences: but 

 it does not furnish tlie means of deciding whether the 

 globe has been peopled from one or more original stocks, 

 nor enable us to trace satisfactorily the mode in which 

 tbeir dissemination has been accomplished. 



Before entering on the immediate object of this section, 

 it is necessary to consider what is the precise acceptation 

 of the terms species and variety in zoology ; what consti- 

 tutes a species, and how varieties arise out of it. 



Animals are characterized by fixed and definite external 

 forms, which are transmitted and perpetuated by genera- 

 tion. The offspring of sexual unions is marked with all 

 the bodily characters of the parents. However strong the 

 impulse may be, which leads to the continuation of the 

 species, there seems to be an equally powerful aversion to 

 intercourse with those of other species. Hence, in the 

 wild state, even the most nearly allied do not intermix ; as, 

 the hare and rabbit ; the horse and ass ; the different kinds 

 of mice, or of rats. Constant and permanent difference, 

 therefore, is the essential notion conveyed by the word 

 species-, and, provided it be invariably maintained, it is im- 

 material whether that difference be great or small. Thus 

 the specific distinction between the black rat (mus rattus) 

 and the brown or Norway rat (m. decumanus), or between 

 the domestic mouse (m. musculus) and the field mouse 

 (m. arvalis), is as perfect as between either of these and 

 the elephant. 



By the reproduction of the same characters, and the 

 aversion to union with other species, uniformity is main- 

 tained ; and the lapse of ages produces no deviation from 

 the original model. Animals are just the same now, as at 

 any, even the remotest period of our acquaintance with 

 them. The zoological descriptions of Aristotle, composed 

 twenty-two centuries ago, apply in all points to the indi- 

 viduals of the present time ; and every incidental mention 

 of animals, or allusion to their characters and properties, in 

 the writings of historians, poets, fabulists, confirms this 



