SEA-SQUIRTS. 323 
Thus the whole family is divisible into two groups, the 
simple and the aggregate; both branching out into numerous 
genera, of which my limits only allow me to mention some of 
the most remarkable. The simple Ascidiz, or Sea-Squirts, are 
very common on our shores. “Rarely,” says Forbes, “is 
the dredge drawn up from any sea-bed at all prolific in 
submarine creatures without containing few or many of their 
irregularly shaped leathery bodies, fixed to sea-weed, rock, 
or shell, by one extremity, or by one side, free at the other, 
and presenting two more or less prominent orifices, from 
which, on the slightest pressure, the sea-water is ejected with 
great force. On the sea-shore, when the tide is out, we find 
similar bodies attached to the under surface of rough stones. 
They are variously, often splendidly, coloured, but otherwise 
are unattractive or even repulsive in aspect. Some are of a 
large size, several inches in length. As may easily be imagined, 
they lead a very inactive life, except in the young state, when 
by means of a long tail they rapidly swim about, until finally 
settling in some convenient spot, they gradually assume the 
form and adopt the quiet life of the parent from which they 
sprang.” 
To the simple Tunicata belong also the Chelyosomata, whose 
coriaceous envelope, consisting of eight somewhat horny angular 
plates, reminds one of the 
carapace of the turtle. 
Their small and promi- 
nent orifices, perforating 
the plated surface, are 
each surrounded by six 
triangular valvules. 
Some species of simple 
Ascidians on the coasts 
of the Channel and the 
Mediterranean are valued Chelyosoma Macleayanum. 
as articles of food. At a. Branchial orifice. 5. Anal orifice, 
c. Coriaceous envelope of the sides. 
Cette sea-squirts are taken d. Stone to which the animal is fixed. 
regularly to market, and Cynthia microcosmus, although so 
repulsive externally, furnishes a very delicate morsel. 
Ri, Pes seek : 
While in the Clavellinide the animals are connected by 
creeping tubular prolongations of the common tunic through 
