. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 108 ANIMAL KINGDOM. system is more concentrated around the en- trance to the alimentary canal in the mollus- cous classes, where it generally forms a trans- verse series of ganglia, disposed around the oesophagus, a character which is expressed by the term cyclo-gangliata. The dorsal position of the great ganglia and nervous columns of the cephalopods, and their partial protection by an organised osseous internal skeleton, leads to the condition of the nervous system presented by the vertebrated classes of animals, where
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 108 ANIMAL KINGDOM. system is more concentrated around the en- trance to the alimentary canal in the mollus- cous classes, where it generally forms a trans- verse series of ganglia, disposed around the oesophagus, a character which is expressed by the term cyclo-gangliata. The dorsal position of the great ganglia and nervous columns of the cephalopods, and their partial protection by an organised osseous internal skeleton, leads to the condition of the nervous system presented by the vertebrated classes of animals, where its central parts are in the form of a lengthened dorsal nervous chord developed anteriorly into a brain, and protected by a vertebral column and cra- nium. The vertebrated classes are thus de- signated spini-cerebrata, from the form of the most influential part of their organization. To the lowest sub-kingdom or cyclo-neurose division belong five classes of animals; viz., 1. Polygastrica, microscopic, simple, transpa- Fig. rent, soft, aquatic animals, in which no nervous filament has yet been detected, generally pro- vided with eyes, with a circular exsertile dental apparatus around the mouth, and with vibratile cilia for respiration and progressive motion, and provided with numerous internal stomachs or cceca communicating with the alimentary cavity. (See POLYGASTRICA.) 2. Porifera, simple, aquatic, soft, animals, without perceptible nervous or muscular fila- ments or organs of sense, with a fibrous internal skeleton sometimes supported with silicious and sometimes with calcareous spicula, the body permeated with a soft gelatinous flesh, covered externally with minute absorbent pores, tra- versed by numerous ramified anastomosing canals, which commence from the pores and terminate in large open vents, as seen in the annexed figure of the halina papillaris, Gr. (Jig. 29), which represents the animal as alive, frf^hrffe!t~ MMffMeifF ^r£gGT ^.-'i-^AV-^.-' '-:^*zL.*
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