on the Natural Group of Tunicata. 529 
commentators, and to lead some of them to believe that his de- 
scription was in fault rather than their own knowledge of Natural 
History. 
The Tunicata have always been interesting to me as an osculant 
group connecting the polype Acrita and acephalous Mollusca. 
That this situation, assigned to them in the Hore Entomologice, 
is natural cannot now for a moment be doubted. Their relation 
to the testaceous Mollusca has been pointed out by Aristotle, 
Baster, Linnzus, Pallas, Cuvier, and Savigny. ‘Their relation 
to the Polypes has likewise been shown by M. Savigny, when he 
demonstrated that the Alcyonium ficus of Linnæus (Alcyonium 
pulmonarium of Solander and Ellis) is nothing else than an aggre- 
gation of minute 4scidic combined in a common envelope. 
_It is rather curious, indeed, to remark, that the affinity of 
these animals to Mollusca, although so early noticed, is less 
striking * to modern naturalists than that affinity which they bear 
to Polypes, and which was only discovered the other day. 
Savigny has distinguished the Tunicata by their having a soft 
test or covering consisting of an organized envelope, provided 
with two orifices, the one branchial, the other analt. By one of 
these orifices the Ascidia imbibes the sea-water and introduces it 
into the branchial cavity ; and every person in the habit of ob- 
serving these singular animals knows that almost the only sign 
of life which they exhibit on being irritated is the spirting out of 
this water from the branchial cavity. But for a general account 
of the structure of that group of Tunicata which comprises the 
* M. de Blainville, however, compares them particularly with the genus Mya. See 
Dict. des Sciences Natur. art. Mollusque, p. 363. 
+ If this character be correct, as there is every reason to believe it to be, the im- 
perfectly known genus Mammaria will, if truly described by Müller, not belong to the 
group, although it has been placed here by M. Lamarck. . There is great obscurity, 
however, hanging over this genus as well as Bipapillaria, which, upon the authority 
of some manuscript notes of Peron, is said to have rigid tentacula. 
Tethya 
