80 Dr Grant on a.Nexv Zoophyte 



nute circular opening is perceived in the centre of the villous 

 surface. The papilla advances from the shell, and its central 

 opening enlarges in proportion to the healthy state of the zoo- 

 phyte, and the purity and stillness of the water ; its flat downy 

 radiated surface gradually diminishes by the widening of the 

 central opening, till only thin margins are left around the orifice, 

 and the current is again seen to play briskly from it. In recent 

 specimens of the Cliona dredged from an oyster-bed neai' the 

 shore at Prestonpans, and examined under the most favourable 

 circumstances on the coast, I have twice observed polypi of ex- 

 traordinary 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, while 

 the current flowed from its central opening. The polypi were 

 perfectly invisible to the naked eye in an ordinary fight and po- 

 sition ; but by suspending the Cliona 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 off a pa- 

 pilla, and placing it under the microscope in sea-water, the polypi 

 continvied their motions, and were seen to consist of a long, slen- 

 der, transparent, cylindrical, tubular fleshy body, at the farther ex- 

 tremity of which were placed about eight short broad tentacula, 

 slightly dilated at their free ends, which were constantly inflect- 

 ing and extending themselves irregularly, while the polypi ad- 

 vanced or retreated. In two entire and fresh specimens, the 

 polypi continued visible and in motion for more than twenty-four 

 hours in a jar of water at Prestonpans ; but I have not yet suc- 

 ceeded in perceiving them in any of the numerous specimens 

 which I have preserved afive in the water procured from New- 

 haven. The spicula of the Cliona celaia are siliceous^ and have 

 a very close resemblance to those of the great Spongia paterce, 

 or Neptune's cups of the Indian ocean, many splendid specimens 

 of which are preserved in the Museum of the University ; when 

 procured separate, by removing the animal matter with the blow- 

 pipe, or with nitric acid, we observe them to be long, slender, 

 cylindrical, tubular, slightly curved, shut at both ends, a fittle 

 fusiform in the middle, acutely pointed at one end, and termi- 

 nated bv a small hollow round head at the other. Thev are 



