SOCIAL ASCIDIANS. 315 
The species of this family are very numerous: 
nearly fifty are enumerated as British; and pro- 
bably not half of the whole number have yet been 
described. One of the most common is Ascidia 
virginea, Which grows to an inch and a half in 
length, and about three quarters in breadth. It is 
pellucid and crystalline, of a pale yellowish tinge, 
revealing through the test the branchial sac, spot- 
ted with crimson, and crossed with lines of white. 
It adheres to stones, dead shells, and living sea- 
weeds in deep water. 
FAMILY CLAVELINADZ. 
(Social Ascidians.) 
In essential points these resemble the preceding 
family, but the individuals are not distinct, but 
united by a common root-thread, from which they 
spring, like buds from a creeping root-stock. The 
thread creeps over the surfaces of stones, the stems 
of sea-plants, &c., continually growing by a length- 
ening of its extremity, and increasing by throwing 
out, either in groups or at regular intervals, a kind 
of buds, that develop into Ascidian mollusks, 
which commonly stand on more or less distinct 
foot-stalks. 
The family may be illustrated by the accom- 
panying figure, greatly magnified, of a tiny species 
(Perophora Listert), found occasionally on our own 
coasts. I obtained the individual from which the 
figure was taken at Ilfracombe, attached to a frag- 
ment of sea-weed. It is, to the naked eye, a 
globule of clear jelly, not larger than a pin’s head, 
yet disclosing, under the microscope, an elaborate 
