Cliona. Z. ASCIDIOIDA. 307 



ter ; its flat downy radiated surface gradually diminishes by the widen- 

 ing: of the central opening-, till only thin margins are left around the 

 onflce, and the current is again seen to play briskly from it. In re- 

 cent specimens of the Cliona dredged from an oyster-bed near the 

 shore at Prestonpans, and examined under the most favourable cir- 

 cumstances on the coast, I have twice observed polypi of extraordi- 

 nary minuteness and delicacy placed around the margin of the orifice 

 and which kept in constant motion, advancing and withdrawing 

 themselves into the substance of the papilla, m hile the current flowed 

 from Its central opening. The polypi were perfectly invisible to the 

 naked eye in an ordinary light and position ; but by suspending the 

 Chona in a crystal jar with clear water, and placing it between the 

 eye and a candle, or the sun, they were seen like filaments of silk or 

 asbestus constantly rising and sinking on the margin of the papilla. 

 On cutting oflf a papilla, and placing it under a microscope in sea wa- 

 ter, the polypi continued their motions, and were seen to consist of a 

 long, slender, transparent, cylindrical, tubular fleshy body, at the far- 

 ther extremity of which were placed about eight short broad tentacu- 

 la, slightly dilated at their free ends, which were constantly inflecting 

 and extending themselves irregularly, while the polypi advanced or 

 retreated. In two entire and fresh specimens, the polypi continued 

 visible and in motion for more than twenty-four hours in ajar of wa- 

 ter at Prestonpans ; but I have not yet succeeded in perceiving them 

 in any of the numerous specimens which I have preserved alive in 

 the water procured from Newhaven." Professor Grant. The spi- 

 cula " are about the fourth of a line in length, and appear through 

 the microscope as minute curved pins spread irregularly through the 

 whole fleshy substance of the animal :" they are " slender, cylin'drical, 

 tubular, slightly curved, shut at both ends, a little fusiform in the' 

 middle, acutely pointed at one end, and terminated by a small hollow 

 round head at the other." Grant. 



Dr Coldstream writes me that, judging from the form of the spi- 

 cula, he believes he possesses another species of Cliona from Bute, 

 perforating the walls of the limpet (Patella vulgata.) 



