370 THE INHABITANTS OF THE SEA. 
and is frequently found in cabinets of natural history, the horny 
and calcareous matter of the axis is disposed in alternate joints, 
50 a3 to unite flexibility with firmness. A similar structure of 
alternately disposed calcareous and horny segments occurs in 
Mopsea. In Isis branches are developed from the calcareous, 
in Mopsea from the horny segments of the axis. 
The Tubiporide are confined to the narrow limits of a single 
genus containing but few species. Here the polypary is com- 
posed of distinct calcareous tubes 
rising from a fleshy or membrana- 
ceous basis, and arranged in suc- 
cessive stages. These tubes are 
separated from each other by 
considerable intervals, but mutu- 
ally support each other by the 
interposition of external hori- 
zoutal plates, formed of the same 
dense substance as themselves, by which they are united to- 
gether, so that a mass of these tubes exhibits an arrangement 
something’ like that of the pipes in an organ, whence the 
beautiful Indian species, Tubipora musica, has derived its 
name. From the upper ends of the tubes the polyps are 
protruded, and being, when alive, of a bright grass-green 
colour, they contrast very beautifully with the rich crimson of 
the tubes they inhabit. 
In our seas, the coralligenous Zoophytarians, distinguished by 
the hard calcareous skeletons they deposit within their tissues 
are but feebly represented by a few straggling Caryophylliz, but 
in the tropical ocean they branch out 
into numerous families, genera, and 
species, and play a highly important 
part in the economy of the maritime 
domain. Originally proceeding from 
single ova, which at first freely move 
by means of vibratile cilia, and 
become fixed after a short period of 
erratic existence, they multiply by gemmation, and grow into 
an immense variety of forms, of which the following descrip- 
tion by one who has long and attentively studied them in their 
native haunts may serve to give an idea. “Trees of coral,” 
Tubipora Musica. 
Caryophylla, 
