ASCIDIZ. | 230 
CLASSIS IV. ASCIDLA. 
Mollusca tunicata, Lamarck. 
Ascidiz, Savigny, Cuvier. 
The external integument of the body is coriaceous or soft, 
very much organized, produced above into two cylindric tubes, 
the one branchial, the other anal. This integument is reflected 
inwardly through the tubes, into which it is produced, and forms 
a very thin serous interior integument. 
The mantle is thin, and lines the inner surface of the inner 
integument and its tubes. The branchize or gills are two, re- 
ticulated, and adhere to the interior walls of the mantle. The 
mouth is a round aperture, sulcated, or furnished with imper- 
fect tentacles, or very small teeth. 
All these animals inhabit the sea. 
General Observations on the genus Ascidia. 
All the animals of this genus are fixed by their base to rocks, 
sand, shells, or even on the bodies of other species of this 
genus. All the species vary much in their form, according to 
the degrees of contraction or dilatation: the surface is smooth, 
tuberculated, mammillated, grooved or folded. 
The animal serving as the type of this class was named The- 
thyrium by Aristotle, who has described its generic character 
nearly as perfectly as any of the modern writers. 
Rondeletius was also acquainted with this genus and its ana- 
tomical structure, but from his rude figures the exact species 
cannot be determined: he calls it Menthula marina. 
Linneus, in his fourth edition of his Systema Nature, has 
converted the name given by Aristotle, Thecthys; and in his 
sixth edition he has confused the Thethys now so named with 
the Ascidie. 
