INTEGUMENT. 691 INTENSITY or SENSATION. Dermal bones and teeth of higher vertebrates liave probably been derived from the dermal bones or bony scales and the tooth-struetures of fishes. Neither Amphioxus nor cyclostomes pos- sess any trace of an exoskeleton. Longitudinal and transverse rows of small denticles are pres- ent in selaeliinns. Each denticle consists of a basal plate and a spine. The dentine of tliis scale is formed by the mesoderm, while the ectoderm forms the enamel w hieh covers the denticle. The fiist impulse toward tooth-formation seems to reside in the derma. The teeth of fishes are fused with the tooth-cement. The teeth of some reptiles lie in sockets in the bone. The teeth of selachians lie in .several rows upon the ujjp.^r and lower jaws. Only one or two of these rows are functional at a time. The outer rows are re- placed from time to time by the younger and in- ner rows-._ In mammals the process of replace- n:ent of teeth is limited in most cases to one occurrence, and the number of teeth is also lim- ited. The gap in the number of teeth in selachi- ans and mammals is bridged by the gradual reduction occurring in intermediate forms. Be- tween scales and the teeth of selachians also in- terniediate forms occur. The dermal bones such as occur in the vertebrate skull, or in the pectoral aich of fishes, are homologous with the basal plates of the dermal denticles of selachians. They arc probably formed by a fusion of such plates. The dermal skeleton is phylogenetically older than the endoskeleton, but it tends gradu- ally to disappear the higher we ascend in the animal scale. Consult: Wiedersheim, Comparative Anatom;/ of Vertebrates (Eng. trans., 3d ed.. .Jena, 180.3) ; Lang. Text-Boole of Comparative Anatomy (Lon- don, ISOl-flO). INTEGUMENT (in plants). A general term, tiut technically applied in seed-plants to the specially developed coat of the o ile. The in- tegument is never absolutely complete, as it leaves at the apex of the o^^lle a small opening through which the pollen-tube enters, known as the 'micropyle.' and at the opposite end of the ovule (chalaza) it is not distinguishiible as a layer. In many cases an ovule has two integu- . nients. See Ovule. INTELLECT (Lat. intellectus, understand- ing, from intellegere, intelligcre, to perceive, from inter, between -|- lefjere, to choose, gather). The common name for the mental processes concerned in the function of cojinition. It is thus the coun- terpart of feeling and will. (See these titles, and .Xfitcction'. ) In the older ]>5ycbologA-. a distinc- tion was drawn, in various ways, between 'high- er' and 'lower' forms of cognition (see Fac- CT.TY), and intellect was thus marked off from sense, or from sense and imagination. "There is nothing in the intellect that has not previously been in sense," says Descartes; but Leibnitz adds, "except the intellect itself." Kant's 'pure intel- lect' is, similarly, an intellect freed in its opera- tion from the intermixture of sense. In modern terminology, intellect covers both sensation and its derivatives: so that its treatment includes the study of the formation of perception and idea, the association of ideas, memory and recognition, passive and active imagination, and reasoning. The word 'intellection' is sometimes reserved for the formation of concepts and judgments and for reasoning; see the discussion of these processes under Logic. The root-function in intellect is discrimination (see DiscBiMisATiox, Sensible), which implies knowledge of the likeness oi similar and of the dilference of dissimilar things, and ( in the case of man) capacity to report in language upon this likeness and difference. The discriminative func- tion is supported and extended by that of repro- duction (see ^Memory), which adds a past and a future to the present domain of mind. Discrimi- luition and reproduction have been variously sub- divided, both upon a genetic and upon a logical basis. Classifications of the latter kind are, how- ever, merely aids to the presentation of psychol- ogy, and do not themselves contribute to our knowledge of mind; while genetic classifications have so far rested rather upon the logic of some psychological system, or upon biological analo- gies, than upon unbia.sed obser-ation of the de- veloping organism. Consult: Bain. The Senses and the Intellect (London, 1868) ; Sully, Human Mind (London, 1892) ; Ladd. Psychology: De- scriptive and Explanatory (Xew York, 1894) ; Titchener, Outline of Psycholotiy (Xew York, 1899). See Animal Psycholocy; Ge.xetic PSYCHOL'JGT. INTELLECTUALISM (from intelUctual, from Lat. intellect ualis, pertaining to the under- standing, from intellectus. understanding). The philosophical theory that the intellect, rather than the alf ections -or the will, is the fundamental process of consciousness, and therefore, on an idealistic interpretation of reality, the ultimate basis and support of all existence. It stands op- posed to voluntaryism and to certain forms of mysticism (q.v. ) which emohasize the episte- nioldtiical and metaphysical importance of the affections. INTEMPEKANCE. See Alcoholism; In- toxication: Drunkenness; Temperance. INTENSITY OF SENSATION (from Lat. inteitsiis, p.p. of iniewh rr, to stretch out, from ill, in -f tendere, to stretch. Ok. reimiv. tcinein, Skt. tan, to stretch). One of the four attributes of sensation, the others being quality, extent, and duration: The intensive aspect of sensation is that "property which enables us to compare it with others in respect to vividness" (Kuelpe). Theoretically every sensation must possess a cer- tain intensity in order to enter consciousness. In the sphere of vision, however, there exist cer- tain facts which make it advisable, according to some p.sychologists, to eliminate the attribute of intensity. Variation of the amplitude of vibration of the stimulus acting upon the retina effects a variation not only in the luminosity, but also, under most conditions, in the color-tone and the saturation of the correlated sensation. Here, then, intensity seems reducible to quality. This is the position of Hering and Hillehrand. On the other hand. Konig maintains that there are two places in the spectrum (the one in the red and the other in the violet) where this does not hold true. G. E. Miiller has. furthermore. sought to overcome the dilliculty by defining in- tensity as degree, the distance of a sensation from the zero-point (apart from qualitative change). If two colors are both reduced, that which reaches the zero-point first has the less intensity. If we add to or subtract from the brightness of a given color quality, we change its
