comparable to divisions; these into families, comparable to regiments; these into genera, comparable to battalions; and these into species, comparable to companies, or ultimate groups of individual units or soldiers. Just as the legions, divisions, regiments, battalions and companies of an army have each their own name or at any rate a distinctive numeral assigned to them in order that they may be cited and directed, so are names given to each class, order, family, genus and species of the classification or enumeration of the kinds of animals and plants. Here, for instance, are the names of the greater and smaller groups in which our common "white" finds itself enrolled. _Class_–Insects. _Order_–Lepidoptera. _Family_–Pieridæ. _Genus_–Pieris. _Species_–brassicæ. CHAPTER VIII MORE ABOUT SPECIES I wrote in the last chapter of the recognition of that degree of "likeness" or kinship in animals and plants which we point to by the word "species," and of the grouping of several similar species to form a "genus," and of several genera to form a family, of families to form orders, and of orders to form classes–and of the giving of names to all these groups. Whilst the making of this or that lot of species into a distinct _genus_, and giving it a new name is a mere matter of convenience for the indication of more or less important agreements and divergences, and is to a large extent arbitrary or an expression of opinion–it has always been recognized among naturalists that the group called "a species" is not a mere convention, but has a real natural limitation. It is true that the actual things which we see in studying natural history are so many units or individuals. But the possibility of arranging these by pattern, colour and shape into ultimate companies of which all the units are alike and differ from all the units of another company, has been regarded as a natural fact of primary importance and not a mere convention or convenience. The conception of the "naturalness" of a species depends really upon a further qualification of great importance as to what we naturalists understand by it.