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 

 O3sophagus, 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 pap'Ularis, Gr. 

 (Jig. 29), which represents the animal as alive, 

 29. 



under water, with the usual currents passing 

 inwards through its pores (a a), traversing its 

 internal canals (6), and escaping by the larger 

 vents (c, d.) (See PORIFERA.) 



3. Polypifera, aquatic animals, of a plant- 

 like form, generally fixed, of a simple internal 

 structure, for the most part without perceptible 

 nerves or muscles, or organs of sense, and nou- 

 rished by superficial polypi, which are developed 

 from the fleshy substance of the body, as in the 

 campanularia dichotoma, (fig. 30), wher^ the 



Fig. 30. 



irritable fleshy tubular portion of the animal is 

 seen to occupy the interior of the base, the 

 stem, and the branches, and to extend in the 

 form of polypi from the open terminal cells. 

 The polypi of most zoophytes are provided 

 with tentacula around their orifice, as seen 

 at B, (fig. 31), and the margins of these ten- 

 tacula are generally furnished with numerous 

 minute processes, termed cilia, (see CILIA,) by 

 the rapid vibration of which, currents are pro- 

 duced in the surrounding water for the pur- 

 pose of attract- 

 ing food and 

 of aerating the 

 surface and 

 fluids of the 

 body, as repre- 

 sented in fig. 

 3, A. (See PO- 

 LYPIFERA.) 

 4. Acalepha, soft aquatic free animals, of a 

 simple structure, generally of a gelatinous and 

 transparent texture, and emitting an acrid se- 

 cretion which is capable of irritating and 

 inflaming the skin like the stinging of a nettle, 

 from which the name of the class is derived. 

 They rarely possess a solid skeleton or a per- 

 ceptible nervous system. They are all marine, 

 often luminous, sometimes they possess eyes 

 with a crystalline humour, they feed on minute 

 floating animals, and swim by the contractions 

 of a highly vascular and irritable mantle or by 

 means of air-sacs, or by the rapid movement of 



