OR OSSEOUS SYSTEM. 1) 



sented in fig. 4 at 2, as alive and cut from its point of attach- 

 ment, c. The circular minute pores by which the streams of 

 water enter the internal tortuous canals are seen all over the 

 surface, as at a #, and the large vents by which the currents 

 issue from the body are seen on the most prominent 

 parts, as at bb. The manner in which the horny filaments 

 are united to each other throughout the whole mass of the 

 body is seen at fig. 4, 1 , where the broken ends of the fibres 

 show their tubular character, and this is still more magnified 

 at fig. 4.* The meshes formed by these horny fibres, though 

 apparently without order or regularity when the soft parts 

 are removed, have the closest relation to the pores and the 

 tortuous canals which wind through every part of the body. 

 Now we see in these simple skeletons of poripherous ani- 

 mals, as in many vegetables still more remote from human 

 organization, that nature begins the formation of an internal 

 framework for the support and protection of the soft parts, 

 by the deposition of detached earthy spicula throughout the 

 cellular substance of the body, as we see in the human em- 

 bryo the deposition of minute spicula of phosphate of lime 

 in various parts of the soft gelatinous bones begins the con- 

 solidation of the skeleton. The abundance of silicious 

 needles in the skeletons of the lowest poriphera assists in 

 their conversion into flint, when their remains have been ex- 

 posed for ages in chalk or other strata traversed by silicifying 

 percolations. 



III. Polypiphera. The skeletons of zoophytes present a 

 great variety of forms and characters, being branched or 

 globular, or filiform, free or fixed, solid, massive, and calca- 

 reous, or soft, flexible, and horny, external or internal. The 

 animals of this class obtaining their food by polypi, or highly 

 organized sacs developed from the fleshy substance of the 

 body, we generally find the skeletons, whether external or 

 internal, to present cavities or cells for the reception and 

 protection of these delicate organs ; and the various forms 

 of these cells constitute a principal distinction among the 

 skeletons of this class. The simplest forms of the skeleton 

 are presented by the horny zoophytes, or keratophytes, 

 where it sometimes consists of tough, soft, flexible filaments 

 which surround the cells of the polypi throughout the whole 

 mass of the body, as in the alcyonium and lobularia. These 

 form a transition from the horny species of poriphera to 



