relatedness which characterize the successive phases of evolutionary progress, inorganic, organic, and superorganic, differ from one another and how they are connected. This one does not find. The impression one gets, here and elsewhere, is that all forms of relatedness must somehow, by the omission of all other specific characters, be reduced to the mechanical type. This, no doubt, is unification of a sort. But is it the sort of unification with which a philosophy of science should rest content? It may be said that unification can only be reached by digging down to some ubiquitous type of relation which is common to all processes throughout the universe at any stage of evolution. But what, on these terms, becomes of evolution itself as a problem to be solved? Surely any solution of that problem must render an account of just those specific modes of relatedness which have been ignored in digging down to the foundations. Surely there must be unification of the superstructure as well as of the substructure. Here and now is our world, within the texture of which things stand to each other in such varied relations, though they may be reducible to a few main types. There, in the faraway part, was the primitive fire-mist, dear to Spencer's imagination, in which the modes of relationship were so few and so simple, and all seemingly of one main type. How do we get in scientific interpretation from the one to the other? Will it suffice to breathe over the scene the magic words differentiation and integration? Spencer appears to think so. Of course he did exceptionally fine work in elucidating the modes of differentiation and integration within certain relational fields--though he sometimes uses the latter word for mere shrinkage in size.[52] But what one asks, and asks of him in vain, is just how, within a connected scheme, the several relational fields in the domain of nature are themselves related, and how they were themselves differentiated. How, for instance, did the specific relationships exhibited in the fabric of crystals arise out of the primitive fire-mist relations? At some stage of evolution this specific form of relatedness came into being, whereas before that stage was reached it was not in being. No doubt we may say that the properties of the pre-existing molecules were such that these molecules could in due course become thus related, and enter into the latticed architecture of the crystal. They already possessed the potentiality of so doing. And if we have resort to potentialities, all subsequently developed types and modes of relatedness were potentially in existence _ab initio_--they were, as Tyndall said, 'once latent in a fiery cloud.' But it is difficult to see how the specific modes of relatedness which obtain within the crystal, can be said to exist prior to the existence of the crystal within which they so obtain.