FLUSTER. 231 



ginous substance, the earthy matter being secreted and deposited in 

 the interstices of a cellular tissue, as in bones. In like manner, some 

 corals yield gelatine upon the removal of the lime, while others afford 

 a substance in every respect resembling the membranous structure 

 obtained by an analysis of the nacreous (pearly) shells. A recent ela- 

 borate analysis of between thirty and forty species of corals, by an 

 eminent American chemist (Mr. B. Silliman), has shown, contrary to 

 expectation, that they contain a much larger proportion of fluorine than 

 of phosphoric acid." 



Flustra foliacea is the broad-leaved Horn -wrack of Ellis ; it is about 

 four inches high, brown, and the polypidom is horny. The cells are 

 small, in alternating rows; sometimes covered by a lid that opens down- 

 wards. Hook says : " For curiosity and beauty, I have not, among all 

 the plants or vegetables I have yet observed, seen any one comparable 

 to this sea-weed." Flustra truncata is abundant in deep water, and 

 grows to a height of about four inches ; it is of a delicate yellow colour, 

 and bushy. The cells have lines in an oblong direction. It is the nar- 

 row-leaved Horn-wrack of Ellis. 



Flustra chartacea. Ellis states : "The cells of this sea-mat are 

 of an oblong square figure, swelling out a little in the middle of each 

 side. The openings of the cells are defended by a helmet-like figure j 

 from hence the polyp-shaped suckers extend themselves. This sea- 

 mat is of a slender and delicate texture, like a semi-transparent paper, 

 of a very light straw-colour. It was first found on the coast of Sussex, 

 adhering to a shell. I have since met, on the same coast, about 

 Hastings, in the year 1765, with several specimens whose tops are 

 digitated, and others that were very irregularly divided." 



Flustra carbasea grows out in a leaf-like manner, gradually widening 

 to the end. It is found on shells of a yellowish-brown colour ; on one 

 of the sides the cells are both large and smooth. The animals have 

 about twenty-two arms or feelers, which Dr. Grant, who has written a 

 most careful paper on these polyps, says, are "nearly a third of the 

 length of the body ; and there appear to be about fifty cilia on each side 

 of a tentacle, making 2200 cilia on each polyp." In this species 

 there are more than eighteen cells in a square line, or 1800 in a square 

 inch of surface ; and the branches of an ordinary specimen present about 

 ten square inches of surface ; so that a common specimen of the F. 

 carbasea presents more than 18,000 polyps, 396,000 tentacles, and 

 39,600,000 cilia. The ova of the F. carbasea make their first ap- 

 pearance as a small yellow point, a little below the aperture of the 

 cell, and behind the body of the polyp ; they are unconnected with 



