being, be enabled to perceive there the process of the growth of this mental necessity in direct correspondence with the evolution of the organism. Through untold ages have the ancestors of man beheld numberless objects break into parts, no one of which was ever as large as the original whole. Through vast geological ages have these facts been impressed upon an evolving mind which, as it never perceived the contrary, had not the data upon which even to imagine it. With this immense induction behind him no wonder, man, when he was able to speculate, asserted the necessary truth of the axiom that "the whole is greater than any of its parts." A necessity for a particular order in nature we know nothing of; that conception arises from the growth of the organism in correspondence with nature as it is.
The old metaphysical conception of types has perhaps had as much influence on scientific controversy as any abstract term. Alike with species, useful when regarded purely as an abstraction from concretes and as an hypothetical form about which to group different individuals, when regarded as a reality it may prove, even in the hands of an able scientist, an ignis fatuus, luring him from the solid ground of scientific knowledge into the quagmires of metaphysical speculation. Like all abstractions, when sufficiently limited in their application, they may lead to useful results, and may suggest resemblances that might otherwise escape the observer. Thus to the conception of types was Goethe indebted for the valuable suggestion he gave to biology. Although these realistic conceptions of abstraction have sometimes brought forth valuable scientific hypotheses, yet their effect commonly has been the reverse. Like the doctrine of final causes, which is popularly supposed to have suggested to Harvey the circulation of the blood, by opening the question as to the use of the valves in the veins, so the doctrine of the existence of types has sometimes been productive of good results; but, as the doctrine of final causes, whatever may be its theological truth, is utterly extra-scientific, and has consequently been a steady opponent of any advance beyond present knowledge, so the theory of types has proved one of the strongest enemies to the acceptance of the theory of evolution. It was his metaphysical belief in this conception that was avowedly the basis of Agassiz's opposition to evolution. Types and species were to him real existences, to which phenomenal existence corresponded. There existed in the universe, for instance, an archetypal form on which vertebrates were modeled. Genera and species corresponded with these types in a greater or less degree, and the assumption that varieties were incipient species which, by successive modifications, could grow into "good species," was, in his view, the introduction of complications into biology sufficient to destroy all classification. Looked at from this standpoint, his vast biological knowledge only served to furnish him with stronger weapons in defense of his position. It may well be doubted whether any proof, however strong, would have been suffi-
