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 fasciae, 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 mo?nus 

 and C.pantex, 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 BoltenicE, 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 oesophagus, 

 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 Ascidida. 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 BotrylUdce, and perhaps the Ascidia globularis of Pallas 

 and Lamarck. It seems necessary for the digestion of Ascidida, 

 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 loop points towards the pedicle. 



In the compound Tunicata of the family of Botryllida 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 



