THE MOLLUSKS. 179 
The gregarious mollusks are sometimes found agglomerated in 
irregular lumps, or sometimes attached to each other singly, like 
the beads of a rosary. The agglomerated mollusks present the 
most curious combinations. The most prominent member of the 
group is, perhaps, the Ascédia, which owes its name to its shape, 
being not unlike a bottle (acxdiov, a leathern bottle). The sub- 
stance of the mollusk is gelatinous, and the association is either 
of a sombre uniform tint, or it is painted with varied hues, which 
are sometimes even brilliant. 
These living associations are found spreading themselves over 
the surface of the submarine rocks, or suspended from the over- 
hanging ledges, like drooping icicles. Sometimes the large fronds 
of wrack which are thrown upon the sand by a storm, are found 
SOCIAL ASCIDIA, 
(Perophora Lister.) 
covered by these curious creatures, which are protected by a glassy 
mantle. Sometimes they bear a fancied resemblance to a starry 
constellation, or they are arranged like a bouquet, or are bent like 
graceful bows of ribbon. The individuals of the group are elon- 
gated or spherical, though occasionally they are angular. When 
one of these animal masses is placed in an aquarium, it appears 
as apathetic as a sponge; the only sign of animation it exhibits 
is a slight movement of the mouths of the orifices. But, upon 
examining it more closely, it is found to be not so inanimate as 
at first supposed, for currents of water go in and out of the orifices 
with such rapidity as to form little jets, if the mollusk be sufficiently 
near the surface. The larve of these animals are single and free. 
At a certain epoch of their existence they become fixed. When 
the little creature has been in its fixed position for some time, 
and has grown suffciently large, there appear upon its surface 
small tubercles, which gradually increase, and in time become 
Me eZ 
