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Show 24 lNTRODUCT ION • . there is a process or phenome- With respect to generatiOn, h d than that of the . n . t 1 ore difficult to com pre en non, m 1m e Y m . f h m We have even seen secr~ti?ns-the pr~~~~~I~:: a~:s~~:c~mprehensible; but the that It IS to be con b . admitted generation presents no exi·s tence of the germ emg . t ' dheres to the parent, I· t particular difficulties. As long as.~ a . d h it de- . . l d . f . t were one of Its organs, an w en IS nour~s le ~s I I 'ts own life which is essentially simi-taches Itself, It possesses 1 ' lar to that of the adult. . The erm the embryo, the fretus, and the new-born am-mai hav~ ne:er, however, exactly the same form. as t~e _ad~lt, and the difference is sometimes so great, that their assimllatio~ has been termed a metamorphosis. Thus, no one not _prev~- 1 f the fact would suppose that the caterpillar IS ous y aware o to become a butterfly· d · h Every living being is more or less me~amorphose m t ~ course of its growth; that is, it loses certain parts, and ~ev~ lo es others. The antennre, wings, and all the parts o_ t e b!terfly were enclosed beneath the skin of the caterpillar; this skin vanishes along with the jaws, feet, and other or~ns, that do not remain with the butterfly. The feet of the rog are enclosed by the skin of the tadpole; and the ta~pol7f~o become a frog, parts with its tail, mouth, and branchire. . e child, at birth, loses its placenta and membranes; ~t a certam . d its thymus gland nearly disappears, and lt gradually perr~ h . teeth and beard. the relative size of its organs acqmres . air, ' ' . · h 'b is altered, and its body augments in a greater ratio t an I head the head more than the internal ear, &c. Th' e place where these germs are found, an d t h e1· r ger ml themselves are collectively styled the ovary; the canal throug~ which when detached, they are carried into the uterus, the ovidu:t; the cavity in which, in many specie~, they ar.e co: pelled to remain for a longer or shorter period pre;IOushe birth, the uterus; and the external orifice through which t t~ pass into the world, the vulva. Where there are sexes, male impregnates, the germs appearing in the female. fecundating liquor is called semen; the glands that ,.,.-....... ~· ·· INTRODUCTION. 25 it from the blood, testes; and when it is requisite it should be carried into the body of the female, the introductory organ is named a penis. Of the Intellectual Functions of .flnimals. The impression of external objects upon the ME, the production of a sensation or of an image, is a mystery into which the human understanding cannot penetrate ; and materialism an hypothesis, so much the more conjectual, as philosophy can furnish no direct proof of the actual existence of matter. The naturalist, however, should examine what appear to be the material conditions of sensation, trace the ulterior operations of the mind, ascertain to what point they reach in each being, and assure himself whether they are not subject to conditions of perfection, dependent on the organization of each species, or on the momentary state of each individual body. To enable the ME to perceive, there must be an uninterrupted communication between the external sense and the central masses of the medullary system. It is then the modi: fic.ation only experienced by these masses that the M~ perceiVes: there may also be real sensations, without the external organ being affected, and which originate either in the nervous chain of communication, or in the central mass itself; such are dreams and visions, or certain accidental sensations. By central masses, we mean a part of the nervous system, that is so much the more circumscribed~ as the animal is more perfect. In man, it consists exclusively of a limited portion of the brain ; but in reptiles, it includes the brain and the whole of the medulla, and of each of their parts taken separately, so that the absence of the entire brain does not prevent sensation. In the inferior classes this extension is still greater. The perception acquired by the ME, produces the image of the sensation experienced. We trace to without the cause of that sensation, and thus acquire the idea of the object that has produced it. By a necessary law of our intelligence, all ideas of material objects are in time and space., VoL. I.-D |
