It is the method of man's bodily organization, and much more, if possible, is it the method of his mental organization. Man's mind consists of powers of affection and thought. His affections, loves, desires, or whatever they may be termed, all group themselves around some leading motive, some ruling passion, which is central for a part or the whole of a lifetime. All minor motives and ends of action are subordinate, and only subservient as a means to satisfy the central, dominant passion. They revolve around it, like satellites around their primary, or like planets around their sun. His thoughts, likewise--the method of his intellectual operations, obey the same law. In every subject which he investigates, he marshals a multitude of facts around central principles or conclusions. He shuts them up under a general, chief, leading fact or law. A number of conclusions, again, are marshalled around one still more general and comprehensive, and thus he mounts up into the highest and most universal principles. All the knowledge stored away in his mind is thus organized, almost without his consciousness, into groups of lower and higher facts and details, ranged under or around their central principles. The closer and more symmetrical is this grouping of particulars and generals in the intellect, or, rather, the greater the power thus to arrange them, the more logical and compactly reasoning is that mind. The looser and less connected is this grouping, the less logical is the mind; and when the proper connection fails to be made between particulars and generals, between facts and their principles, or between parts and their centre, then the mind is in an idiotic or insane condition. Now, man's mental movements, being thus themselves obedient to this great order-evolving method, then, of course, when he applies his faculties to investigate the objects and phenomena of the outer world, he classifies, arranges, and disposes them strictly after the same method, because he cannot help doing so. The naturalist studies minerals, plants, animals--and each kingdom, at his bidding, marshals itself into order before him. Each resolves its otherwise confused hosts into groups and series of groups, each with its own centre and leading type. The animal kingdom has its sub-kingdoms, classes, orders, families, and species. Botanists speak of divisions, classes, orders, genera, and species, &c., species being the first assemblage of individuals.