122 ITS STRUCTURE. 



conical stone, the whole being nine or ten inches in 

 height. The basal stone is densely covered with 

 parasitic Zoophytes, and tubicolous Annelides of 

 many species. 



But our admiration of this handsome Ooral is much 

 heightened when we know something of its nature. 

 We see that its walls, which are not more than one 

 thirtieth of an inch in thickness, are composed of 

 stony substance, yet very brittle. Closer examina- 

 tion shows that this thickness, small as it is, in- 

 cludes two ranges of cells, which are placed back 

 to back, opening by oval orifices on both sides of 

 the walls. 



Every cell is inhabited (or rather has been, for the 

 older ones are dead and vacant before the younger 

 are formed) by an active Polype of the Bryozoan 

 Class, whose head, crowned with a funnel of radiating 

 ciliated tentacles, protrudes from the orifice oris with- 

 drawn into it at pleasure. These all are united by a 

 common life ; a common bond of sensation and of 

 nutrition connects the whole of the individuals into 

 one compound being. A single Polype, inhabiting a 

 solitary cell, began the colony, which has grown by 

 the continual formation of new individuals on every 

 side, as buds grow into branches, which bud again 

 and form a tree. 



Some idea of the populousness of such a commu- 

 nity may be gathered from the following calculations. 

 I took a piece from my specimen, on which I carefully 

 marked out an area of one eighth of an inch square. 

 Within this I found the orifices of 45 cells; as the 

 rows are double, this would give 90 cells in every 



