ANTHOZOA ASTEROIDA. 159 



slightly curved and bulged, closely compacted yet distinct, and of a 

 red colour ; for the colour of the zoophyte is derived from them, and 

 they are accordingly less numerous where the purple is faint or de- 

 fective. They are apparently inorganic and calcareous, being dis- 

 solved, with effervescence, in the mineral acids.* Their form and ar- 

 rangement is the same in every part of the skin ; and the papillae on 

 the back of the rachis, as well as the polype-cells, are constructed of 

 them, but none can be detected in the subcutaneous uncoloured 

 gelatinous flesh. 



The stalk is hollow in the centre, and contains a long slender 

 bone, which is white, smooth, square, and tapered at each extremity 

 to a fine point. It seems intended to stiffen the polypidom, but it 

 does not extend the whole length of the stalk, for before it reaches 

 either end, the point is bound down and bent backwards like a shep- 

 herd's crook. It consists, according to Sir E. Home, of phosphate 

 and carbonate of lime, making thus a near approach to the bone of 

 vertebrate animals. Lect. Comp. Anat. i. p. 59. 



The papillae on the back of the rachis, and between the pinnse, are 

 disposed in close rows, and do not differ from the polype-cells except 

 in size. The latter are placed along the upper margin of a flattened 

 fin ; they are tubular, and have the aperture armed with eight 

 spinous points, which are moveable, and contract and expand at the 

 will of the animated inmates. These are fleshy, white, provided with 

 eight rather long retractile tentacula beautifully ciliated on the inner 

 aspect with two series of short processes, and strengthened moreover 

 with crystalline spicula, there being a row of these up the stalk, 

 and a series of lesser ones to the lateral ciliae. The mouth, in the 

 centre of the tentacula, is somewhat angular, bounded by a white li- 

 gament, a process from which encircles the base of each tentaculum, 

 which thus seems to issue from an aperture. The ova lie between 

 the membranes of the pinnae ; they are globular, of a yellowish 

 colour, and by a little pressure can be made to pass through the 

 mouth. 



Bohadsch says that the Pennatulse swim by means of their pinnae, 



* Dr. Coldstream, of Leith, on whose observations I place a greater reliance than 

 on my own, writes me thus : " The spicula of the Pennatula appear to me to be 

 solid. I have examined them with high powers, after having exposed them to a 

 high temperature, and have not been able to see any evidence of a cavity within ; 

 whether viewed with reflected or transmitted light, they seemed to be opaque. When 

 connected with the body of the animal, they certainly seem to be red ; but a slight 

 degree of heat is sufficient to bleach them." 



