Perhaps, then, it will be best to treat generically the universal attributes of the groups that have a common nature and contain closely allied subordinate forms, whether they are groups recognized by popular usage, such as Birds and Fishes, or groups not popularly known by a common appellation, but composed of closely allied subordinate groups; and only to deal individually with the attributes of a single species, when such species man, for instance, and any other such, if such there be are not of that sort.