Little work has been done on metamorphosis in other animals. In caterpillars the brain produces some chemical substance neces sary for pupation (Kopec). Certain treatments will cause the meal-worm beetle to develop large wing-rudiments while still in the grub stage; apparently the relative growth-rate of the wings has been altered. In sea-urchins J. S. Huxley has secured precocious metamorphosis by immersing moderately-advanced larvae in very dilute poisons for some hours. The larval tissues are much more affected by the poison, undergo dedifferentiation (q.v.) and can then be absorbed by the urchin-rudiment. Here it is probable that no hormone is concerned with metamorphosis. Ascidian larvae metamorphose precociously under thyroid treat ment (Weiss), but lamprey larvae do not. Metamorphosis is thus accomplished in different ways in different animals. (J. S. H.) METAPHOR, a figure of speech, which consists in the trans ference to one object of an attribute or name which strictly and literally is not applicable to it, but only figuratively and by analogy. It is thus in essence an emphatic comparison, which if expressed formally is a "simile"; thus it is a metaphor to speak of a ship ploughing her way through the waves, but a simile when it takes the form of "the ship, like a plough, moves," etc. METAPHYSICS. The systematic study of the fundamental problems relating to the ultimate nature of reality and of human knowledge. It naturally falls into two divisions, namely, Ontology or the systematic study of the ultimate problems of Being or Reality, and Epistemology, or Theory of Knowledge, the sys tematic study of the ultimate problems of human knowledge. These constitute between them the principal departments of Phil osophy, which, however, also includes certain other branches of inquiry which are commonly known as philosophical studies or sciences (Ethics, Logic, etc.). (See PHILOSOPHY.) Few systems of philosophy do even justice to both departments of Metaphysics. With rare exceptions, like Plato, the Sceptics, Descartes and Locke, philosophers before the time of Kant's Critique of Pure Reason (I781) were mainly interested in ontology. Since the time of Kant, however, metaphysical interest has shifted to a very large extent to Epistemology. For sceptics and agnostics of course, there can be no such thing as ontology, and even Kant and his school are essentially agnostic in relation to ontology, except as a matter of faith based on moral postulates. These facts may help to explain the vacillating use of the term Metaphysics. Some writers use it as synonymous with Ontology, others make it synonymous with Epistemology. But if due regard is paid to the whole history of the subject there can be no reasonable doubt that the correct use of the term is to make it include both Ontology and Epistemology, or Theory of Being and Theory of Knowledge, as its two intimately related branches. Metaphysical speculations are the outcome of what is called sometimes a "re ligious impulse" and sometimes a "metaphysical craving" to find something permanent behind or beyond the changing appearances of daily observation, and to acquire a knowledge that shall be better founded than the shifting opinions usually encountered.
The first introduction of the term Metaphysics was a mere accident. When the writings of Aristotle were first collected and arranged by Andronicus of Rhodes (in Rome, about 7o B.c.), or possibly by some earlier Peripatetic already, the treatises on what Aristotle had called "First Philosophy" (also "Theology") were placed after the treatises on physics, and so came to be known as "the treatises after the physical treatises" (TILAETILTa (IMMILKIL) In course of time this designation was applied to the subject matter of these treatises, and so the Scholastics used the term transphysica for studies which come after the ordinary physical studies of natural phenomena. The term Metaphysica occurs already in Boetius (A.D. 48o-525). To some people the term "metaphysical" rather suggests the "supernatural." This is partly responsible for the growing unpopularity of the term, and for the increasing tendency to use the wider terms "philosophy" and "philosophical" in place of "metaphysics" and "metaphysical." As the principal types of epistemological theory are dealt with in the article on KNOWLEDGE, THEORY OF, it is only necessary to set out here the main types of ontological theory (see ONTOLOGY). Briefly, these are : (I) One of the first questions, probably the first question, raised in the history of Western philosophy was, Is there any thing permanent at the basis of the changing phenomena of Nature? The earliest Greek philosophers (Thales, Anaximander, etc.) assumed that there is; so did many subsequent philosophers
(the Eclectics, Plato, Aristotle, Spinoza, etc.). On the other hand, Heraclitus, among the ancients, and Bergson and James, among the moderns, maintain that there is nothing permanent, that the "ever rolling stream" of changing phenomena or of experiences is the only and ultimate reality.' We may call a philosophy of the former type Ontological Substantivalism; one of the latter type Ontological Phenomenalism. The latter view implies epistemo logical phenomenalism, but is not necessarily implied by it.
(2) The second question is as old as the first, and may be put in this way. Is there only one ultimate reality or more than one? The possible answers to this are obvious. They may be expressed by the familiar terms, Monism and Pluralism, corresponding re spectively to the views that ultimate reality is just one, or more than one. Thales, the Eclectics, Plato, Spinoza may be classed as Monists. Democritus and the Atomists, Descartes and Leibniz may be classed as Pluralists. To avoid confusion with the other uses of these terms, it may be advisable to call these views Sub stantival Monism, and Substantival Pluralism respectively.
(3) The third problem, also old, is whether ultimate reality is all of one kind only or of more kinds than one. Here, too, the possible answers are obvious. Moreover, Substantival Monism clearly implies the former alternative. On the other hand, Sub stantival Pluralism may or may not adopt the same alternative. Leibniz, e.g., was a pluralist, but the monads in which he believed were all supposed by him to be of the same (spiritual) kind, only different in degree. Similarly with the Atomists. On the other hand, Descartes (if one can really be sure about his views) be lieved in a plurality of material substances, and a plurality of souls or mental substances entirely different from the material sub stances, and in God besides. To name these distinctions suitably is not easy. Since they affect Pluralism only, one might dis tinguish between uniform pluralism (like that of Leibniz) and multiform pluralism (like that of Descartes) ; Substantival Monism being necessarily uniform.
(4) The fourth question relates to the number of fundamental or irreducible attributes which pertain to the real or reals. To this question likewise the answer may be "one," or it may be "more than one." If "one," we have Attributive Monism (Leibniz, on the one hand, the Materialists, on the other, also the Volun tarists) ; if "more than one" then we have either Attributive Pluralism (Spinoza, for instance) which recognizes a multiplicity or even an infinity of such attributes, or Attributive Dualism or Natural Realism (like that of Descartes and of some modern realists) which recognizes only two such attributes, and may associate each of them with a different kind of substance. At tributive Monism is known as Materialism, if materiality or extension or some form of physical energy is the only irreducible character admitted; it is called Ontological Idealism or Intellec tualism or Spiritualism if thought or reason or some sort of in telligence is the only irreducible attribute that is acknowledged; it is called Voluntarism if the irreducible attribute is identified with will (e.g., Schopenhauer and Nietzsche) ; it is known as Neutral Monism if the ultimate attribute is regarded as different from both mentality and materiality, but as the source of the emergence of both (e.g., W. James, B. Russell and some of the New Realists). E. von Hartmann's philosophy of the unconscious must probably be classed as a form of Attributive Dualism be cause the "Unconscious" is conceived by him apparently as a combination of will and unconscious or subconscious cognition. Materialism usually regards mentality (or consciousness in the widest sense of the term) as a mere epiphenomenon or by-product of matter or physical energy; and Ontological Idealism as com monly treats so-called material objects and events as mere ap pearances to, or creative images of, some consciousness or other. It should be remarked, however, that there is a very modern type of Idealism which is not primarily epistemological nor ontological, but axiological, maintaining simply that it is the "ideal" or rational part of reality which is the most valuable. Such a view is, of course, compatible with most ontological theories.