species which are also coordinate. Usually there are found to be more subdivisions than these and we have in botany at least, suborders, subfamilies, tribes, subtribes, and subgenera. Even species have their varieties, and in some sciences, particularly in ornithology, these are called subspecies and have a special significance. What most concerns us here is that in characterizing these sucessively lower and lower groups, when scientifically done, none of the characters are described in a lower that have already been employed to mark off the next higher group. All the characters of a family are additional to those of the order to which it belongs, all those of a genus additional to those of its family, and all those of a species additional to those of its genus. In correct synoptical work there is no repetition or mixing up of the characters belonging to these respective groups, so that we speak of ordinal, family, generic, and specific characters.
All this may at first sight seem irrelevant to the question before us, but natural history furnishes the best possible example of the primary process of the mind in reasoning upon concrete facts. There is a certain school of biologists who are somewhat disposed to sneer at the old-fashioned study of systematic botany and zoölogy, but if it had no other claims it could be defended from the pedagogic standpoint as the best possible discipline of the mind, as the supreme object lesson in logic. It may sound paradoxical to assert that the study of living organisms can be made an aid in grasping the abstruse problems of metaphysics, but it certainly can do this. One of the most difficult of those problems has always been the Platonic idea, and few students ever readily grasp it. Yet every one of these groups in natural history classification to which I have referred is nothing more nor less than a Platonic idea. A species, a genus, a family, an order, a class or a kingdom is this and nothing else, and every schoolgirl who has analyzed a flower has, unknown to herself and without mental effort, obtained a clear conception of what constitutes the Platonic idea.
We come then to the last and highest of the sciences, viz., sociology, and what has been said is calculated to prepare us
