. A manual of zoology. Zoology. 114 GENERAL ERIXCIPLES OF ZOOLOGY. The Tubular System is fouiul only in Ihe chordatcs (lig. 79). The vertebrate brain and spinal cord form a tuljc with greatly thickened walls. In the centre lies the extremely narrow central canal, which wiiiens anteriorly into the ventricles of the brain. In a transverse section the nervous elements are seen grouped arountl the central canal in a manner almost the reverse of that of the ganglionic type. On tlie periphery lies a layer of nerve-tibres (the icliilc mailer); next is a central portion formed of ganglion-cclls and ne
. A manual of zoology. Zoology. 114 GENERAL ERIXCIPLES OF ZOOLOGY. The Tubular System is fouiul only in Ihe chordatcs (lig. 79). The vertebrate brain and spinal cord form a tuljc with greatly thickened walls. In the centre lies the extremely narrow central canal, which wiiiens anteriorly into the ventricles of the brain. In a transverse section the nervous elements are seen grouped arountl the central canal in a manner almost the reverse of that of the ganglionic type. On tlie periphery lies a layer of nerve-tibres (the icliilc mailer); next is a central portion formed of ganglion-cclls and nerve-hbres (the gray matter), \\\\\d\ is marked off from the central canal b_v a special epithelium (cpciidyma). In addition there are modified sup- porting cells which form a frame- work {glia, neuroglia) for the nervous parts. Relations of Nervous System and Skin.âIt has been ascer- tained in almost all animals that ///(â )!ervenis svsle}ii arises jrom tlie cetoderin. Therefore, in many animals, the nerve-cords and the ganglionic masses lie permanently in the skin; in others only during the development, later becoming separated by splitting of! or by infolding, and thus coming to lie in the deeper layers of the hoAy (fig. 9). In the vertebrates and some other higher animals, besides the body nervous system, there is a sympa- ihetie system for the control of the vegetative organs which are not intluenced Ijy the will. III. Sensory Organs. \Miat we know of the external world is founded upon experiences gained through our sensory organs, controlled by the judgment. If things exist outside of ourselves which have no inlluence upon our senses, we can form no conception of ibem. Il follows from this pro|Hisition that we can gain knowknlge of the capacity of the sensory organs of animals only by analogy with our own experiences. Elence the distinction of five senses, touch, taste, smell, hearing, and sight, liased upon human pln'siol- logyhas l)een extended to the whole animal king
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
