2 PORIPHORA. 



Recent observations made by Mr. Bowerbank 

 have shown that these currents are produced by 

 cilia or whip -like threads within the canals, which 

 maintain a waving or lashing motion in a given 

 direction. The canals themselves are formed by 

 the arrangement of the fibres which give solidity 

 to the Sponge, and these are either horny, variously 

 branched and interlaced, or crystal-like, composed 

 of lime or flint, and resembling in shape needles, 

 pins, or stars. These bodies (spicula) often exist 

 in immense numbers. Both the fibres and the 

 spicula are invested with a glairy coat of living 

 jelly, which is the organic or fleshy part, but 

 which has so little consistence as often to run off 

 in streams when the Sponge is taken from its 

 element. 



Localities, &c. — The surfaces of rocks, the under 

 sides of stones at low water, the interior of caverns 

 that are washed by the tide, and various objects 

 from deep water, are generally coated with Sponges 

 of many species; and some of the more delicate 

 adhere to sea-weeds. The curious genus Cliona 

 inhabits branching cavities in shells, which it lines 

 with its bright yellow flesh : these cavities it 

 excavates by the aid of the sharp angles and cut- 

 ting edges of the flinty granules which stud its 

 surface, as has been proved by Mr. Albany 

 Hancock, who has greatly added to the number of 

 known species. 



Identification. — The texture, whether compact 

 or loose, woody or spongy, woolly or gelatinous ; 

 the general form; the surface; the orifices; and in 

 particular the spicula, whether composed of flint 

 or lime (to be determined by testing them with 

 acids), and whether simple or starred; and, if the 



