306 
Z. A8CIDIQIDA. 
Cliona. 
laris, and, like it, is almost entirely composed of siliceous spicula, 
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 ramificat ions, 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a needle, or withdrawn from the water, the opening gradually closes, 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tract, is withdrawn completely within the aperture of the shell.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- 
4 
