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 AscidisB, or Sea-Squirts, are 

 very common on our shores. "Barely," 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 

 as articles of food. At 

 Cette sea-squirts are taken 

 regularly to market, and Cynthia mdcrocosmus, although so 

 repulsive externally, furnishes a very delicate morsel. 



While in the Clavellinidse the animals are connected by 

 creeping tubular prolongations of the common tunic through 



Chelyosoma Macleayanura. 

 a. Branchial orifice. 6. Anal orifice. 



c. Coriaceous envelope of the sides. 



d. Stone to which the animal is fixed. 



