ORGANIC AND INORGANIC MATTER COMPARED. 77 



threads being cased with a tubular sheath of 

 horn, which they themselves have secreted by 

 way of support and defence. " Let us picture 

 the whole as a tuft of delicate vegetation, a 

 frondescent plant of a tubular horn, with 

 orifices, or cups, or bells, bestudding every 

 branch in which the polypes reside, and from 

 which they can protrude their contractile tenta- 

 cles. Such have we in the Sertularicc, com- 

 pound tubular Phytozoa, which we find rooted 

 to stones and shells in abundance on our own. 

 coast." " There are, however, some Phytozoa 

 which inhabit calcareous tubes, and in some 

 instances these tubes are collected into masses 

 of considerable extent, all ranged in order, like 

 reeds bound together, or the pipes of an organ. 

 They are open at one end, through which the 

 polypes, independent of each other, except when 

 they form the bands or stages which unite the 

 pipes together, protrude their flowerets. Such 

 is the beautiful Tubipora musica of a deep red." 

 Distinct alike both from the cortical and the 

 tubular Phytozoa are the Alcyonida;. In these 

 we find neither a horny or calcareous axis, nor 

 a horny or calcareous sheath, but are here pre- 

 sented with a firm cartilaginous mass, having 

 calcareous $picula> ) at least in some instances, 

 dispersed through its substance. This mass is 

 studded with flower-like polypes, each in its 

 own cell, the cells being excavated in the living 

 gelatinous mass, to the nutriment of which, as 

 the common bond of union between them, they 

 all contribute. These may be called compound 



