on the Natural Group of Tunicata. 539 
these viscera are enveloped in a mantle, of which the summit 
is prolonged and fills the interior of the pedicle, as Savigny 
says, like a marrow. The muscles with which the mantle is sup- 
plied are very narrow circular fasciæ, crossing each other at 
very oblique angles, and may thus be easily distinguished from 
the nervures of the branchial net. The internal structure of 
Boltenia reniformis is, in short, so near that of Cynthia momus 
and C. pantez, that the generic difference which M. Savigny has 
stated to exist between them rests principally on their external 
structure, and the presence or absence of a pedicle. 
It is easy for the naturalist now to perceive that those figures 
of Boltenie, which represent them as supported vertically on a 
rigid peduncle, give them an unnatural position; that is, a posi- 
tion where the branchial pouch, and consequently the cesophagus, 
instead of descending, ascend. "The pedicle, indeed, is clearly 
flexible in a natural state, in order that its drooping by the 
weight of the body may give this last a position analogous to 
that of other Ascidide. When such animals exist, supported by 
a rigid peduncle, this must be inserted at the other extremity of 
the body, as in the genus Clavellina of Savigny, the compound 
family of Botryllide, and perhaps the Ascidia globularis of Pallas 
and Lamarck. It seems necessary for the digestion of Ascidide, 
if, at least, we may judge from their general construction, that 
the intestinal canal should form a loop or ansa. This loop, how- 
ever, may be either ascending, as in Boltenia, or descending, as 
in Clavellina; the only circumstance common to both genera 
being, that the /oop points towards the pedicle. 
In the compound Tunicata of the family of Botryllide the 
pedicle seems to be a receptacle for the eggs, as in certain Cirri- 
pedes. In Clavellina it may possibly be the same; but whether 
it be also the case in Boltenia is not so certain. 
VOL. XIV. 4 A The 
