306 Z. ASCIDIOIDA. Cliona. 



laris, and, like it, is almost entii'ely composed of siliceous spiciila, 

 which are straight and in shape like a pin, but from their brittleness 

 few can be separated from the mass in an entire state, and we seldom 

 observe one with the enlargement that takes the place of the head. I 

 have examined specimens in oysters brought to market, and having 

 placed these in sea water, other fellow parasites of their own class 

 soon gave evidence of their being yet living and active, but I had 

 never the pleasure of seeing the polypes of this production. 



" The Cliona in the living state consists of a soft, fleshy, granular 

 and distinctly irritable substance, of a greenish yellow colour, tra- 

 versed, like many other zoophytes, with minute and regularly formed 

 spicula. Its form depends on that of the cavities which it fills ; it 

 insinuates itself into their minutest ramifications, and adheres so close- 

 ly to their smooth parietes, that it cannot be separated without tearing. 

 The parts of the Cliona which project through the holes on the sur- 

 face of the shell are tubular ; and on removing the outer layers of 

 the shell, we can perceive several empty canals winding and ramify- 

 ing from these tubular papillae, through the body of the zoophyte. 

 During the months of March and April, when these observations 

 were made, numerous small yellow ova were seen in the vicinity of 

 the canals, agreeing much in their form, colour, size, and mode of 

 distribution with those of the Spongia papillaris and Spongia pani- 

 cea, which were then nearly in the same stage of advancement. The 

 projecting tubular papillae possess a complicated structure, and a high 

 degree of contractile power, and exhibit a singular series of appear- 

 ances, when the zoophyte is attentively examined while at rest in pure 

 sea water. When under water, the papillae are seen projecting from 

 the apertures of the shell, sometimes to the length of a line and a 

 half ; they present a wide circular opening in their centre, and a rapid 

 current of water issues constantly from them, conveying occasional 

 flocculi of a grey membranaceous matter. But on being touched with 

 a needle, or withdrawn from the water, the opening gradually closes, 

 the current ceases, and the whole papilla continuing slowly to con- 

 tract, is withdrawn completely within the aperture of the shell. The 

 papillae, viewed in their contracted state, present a smooth, rounded, 

 shut extremity ; but when they begin to advance beyond the surface 

 of the shell, their extremity becomes flat and slightly dilated, assumes 

 a villous appearance, with open fissures, radiating from the centre to 

 the margin of the papillae, and at length a minute 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 zoophyte, and the purity and stillness of the wa- 



