on the Natural Group o/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 Hora Entomologies, 

 is natural cannot now for a moment be doubted. Their relation 

 to the testaceous Mollusca has been pointed out by Aristotle, 

 Baster, Linnaeus, Pallas, Cuvier, and Savigny. Their relation' 

 to the Polypes has likewise been shown by M. Savigny, when he> 

 demonstrated that the Alcyonium Jicus of Linnaeus {Alcyonium, 

 pulmonarium of Solander and Ellis) is nothing else than an aggre- 

 gation of minute Ascidice combined in a common envelope. '' 



It is rather curious, indeed, to remark, that the affinity (rf 

 theses 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 Mi/a. See 

 Diet, des Sciences Natur. art. Mollusqve, p. 363. ■ ' • = 



t If this character be correct, as there is every Veason to believe it to be, the im- 

 perfectly known genus Mammaria will, if truly described by Miiller, 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 



