ALCYONIUM. 45 



But my observations on them have been inconclusive and unsatis- 

 factory, so that I feel much embarrassment in assigning such peculiarities 

 as may be due to each variety — farther than describing all as ascidian : 

 the body long and slender, and provided with a circle of tentacula, ranging 

 from 12 to 18 in the adult. 



There must be undoubtedly an immense disproportion in the dimen- 

 sions of the hydra? of different specimens comparatively, on reflecting that 

 the minute specimen, fig. 1, exhibited several, as seen by fig. 2, where we 

 should not have supposed there was room for any. 



The surface of some specimens, certainly the Alcyonium gelatinosum, is 

 composed entirely of polygonal, pentagonal, or hexagonal compartments, 

 forming cells, each occupied by a hydra. Such was the structure of the 

 specimen, Plate XIV. ; whose compartments are seen, Plate XVII., 

 figs. 6, 7. Also of another, just alluded to, as ten inches and a half high, 

 seated on the Venus Islandica. This was of a fine translucent green, full 

 of irregular white specks imbedded in the surface. On a favourable view 

 the cells of the specimen Plate XIV., seemed to have prominent edges. 

 Some were regular, others irregular. The hydra; had 15 or 16 tentacula. 

 Those of a specimen, whereof all the parts were round, amounted to 12 ; 

 and the hydra; of another, exactly resembling the Alcyonium represented 

 by Ellis, Plate xxxii. d, had about the same number. 



It rather appears that this particular number is peculiar to a papillar 

 surface, such as authors ascribe to the Alcyonium liirsutum. In a speci- 

 men, Plate XVII. fig. 5, which I could neither identify with it, nor re- 

 ject, the hydrse had 16, 17, 18. Those of fig. 3 of the same plate, had 

 about 15. On the animals retreat, the surface of both these specimens, 

 fig. 3 and fig. 5, the surface remained papillous. 



Thus I am induced to entertain some doubt whether there is any 

 strict uniformity in the number of tentacular organs among the Alcyonic 

 tribes. At least I should wish farther opportunities of investigating the 

 fact. 



As the water becomes vitiated the hydras drop from their cells, owing 

 either to decay of the parietes, or of the connecting ligaments. 



All the Alcyonia which I have seen were of various shades, of trans- 



