pretative as well as observational, synthetic and constructive as well as analytic. In its vivid realization of the correlation of organisms, this " study in faunal evolution " continues the tradition of Darwin.
Mechanism atid Vitalism. Coming finally to the " Magnolia Naturae," and the diverse attitudes of modern zoologists to these, as in the long controversy of mechanists and vitalists, we cannot yet say that substantial conclusions have been reached. The conflicts between mechanistic and vitalistic interpretations, between the purely physiological (i.e. apsychic) and the psycho- biological descriptions of behaviour continue with undiminished vigour. Yet there is progress in the fact that the questions at issue are being denned with increasing precision, (a) Everyone allows that there is a chemistry and a physics of the organism; that a chemical and physical (i.e. theoretically mechanical) description can be given of much that goes on in the living body; that the chemical and physical analysis of the animal has yielded very important results; and that this kind of description will certainly extend its scope, (b) It is widely though not unani- mously held that there is little help in the hypothesis that a special form of energy (" vital " or " biotic ") comes into operation in organisms, and is convertible into equivalent quantities of other forms of energy. For no one has demonstrated this specific vital energy, much less measured its intensity. As the tendency of science is to greater simplification of the forms of energy, we must agree with Bayliss (1915, p. 31) that "it seems somewhat retrograde to assume a new form of energy, especially as there is no urgent necessity for it. The resources of the known forms of energy are not altogether exhausted." (c) Many physiologists occupy the position of Claude Bernard: " There is in reality only one general physics, only one chemistry, and only one mechanics, in which all the phenomenal manifestations of nature are included, both those of living bodies and those of inanimate ones. In a word, all the phenomena which make their appearance in a living being obey the same laws as those outside of it " (La Science Experimental, 1878, p. 116). (d) There is, however, a growing body who hold to what may be called methodological vitalism. Without presuming to set limits to the extent to which chemical and physical descriptions may be given of what occurs in a living animal, and without assuming that the concepts of physics and chemistry are stationary (which they certainly are not), it is urged that up to the present the chemico-physical interpretation remains inadequate. For there has not been given any exhaustive physico-chemical description of any total vital operation, such as the contraction of a muscle, still less of any complex case of animal behaviour. And as to individual development we cannot give a mechanical description of the condensation of the inheritance into a germ-cell, nor of the differentiation of the embryo, nor of the regulation phenomena observed when an embryo rights itself after the building materials of its living edifice have been seriously disarranged, nor of the way in which many developing parts seem to conspire toward one result. Similarly as regards organic evolution: we cannot offer a rriechanical theory of variability; and the process of selection is much more than mechanical sifting. In short, mechanical formulae do not fully suffice for answering biological questions. Biology requires Categories of its own. (e) But when the critic of mechanism advances beyond this, to postu- late some further vital agency associated with the organism, operating actively in certain cases, directing the chemico- physical processes so that their results are different from what they would have been apart from its intervention, he has passed to thoroughgoing vitalism. Bergson's " elan vital " has much of this character; but the most consistently thought out expres- sion of this doctrine is Driesch's " Entelechy " (The Science and Philosophy of the Organism, 2 vols. 1908). Discussions of the problem of vitalism may be conveniently found in John- stone's Philosophy of Biology (1914), and Thomson's System of Animate Nature (2 vols. 1920). See also J. S. Haldane (Organism and Environment, 1917) in which he discusses the physiology of respiration as a test case, and with suggestiveness for both sides of the controversy.
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ZUIDER (or Zuyder) ZEE (see 28.1049). It was after the draining of several landlocked seas and small sea-arms of the province of North Holland had been successfully completed in the early part of the i7th century that, about the middle of the next century, the idea of the shutting off and draining the entire Zuider Zee first began to be discussed. Serious objections to the initial scheme led to various proposals for the draining of parts of that sea, and eventually to a thorough investigation as to the best means of closing and draining it. This
