114 MOLLUSCA. 



Some species are remarkable for the long pedicle which supports 

 them*. 



FAMILY II. 



AGGREGATA. 



The second family consists of animals more or less analogous 

 to the Ascidiae, but united in a common mass, so that they 

 seem to communicate- organically with each other, and in this re- 

 spect to connect the Mollusca with the Zoophytes ; but independently 

 of their peculiar organization, these animals, according to the observa- 

 tions of Messrs. Audouin and Milne Edwards, at first live and swim 

 separately, only becoming united at a certain subsequent period, a 

 fact which is in direct opposition to this opinion. 



Their branchiae, as in the Ascidise, form a large sac, traversed by 

 the aliment before it arrives at the mouth ; their principal ganglion 

 is also situated between the mouth and the arms; a nearly similar 

 disposition obtains with respect to the viscera and ovary f . 



Notwithstanding this, some of them, like the Biphora, have an 

 opening at each extremity. Such is the 



BOTRYLLUS, Gcert., 



Of an oval form, fixed on various bodies, and united by tens or- 

 twelves, like the rays of a star. The brianchial orifices are at the 



'ITie Astidia canina, Mull., Zool. Dan., Iv, Asc. inlestinalis, Bohatsch, X, 4, and 

 perhaps even the Asc. patula, Mull., Ixv, and A. corrugata, Id., Ixxix, 2, appear to 

 form but one species. There are also some interversions of synonymes, and the 

 species, generally, are far from being well ascertained. 



M. de Savigny has endeavoured to subdivide the Ascidise, Mem. sur les Anim. 

 sans, vert., part II, 1816, into several subgenera, such as, 



1st. The CYNTHI^E, whose body is sessile, and branchial sac longitudinally pli- 

 cated ; their envelope is coriaceous ; 



2d. The PHALLUSi^,which differ from the Cynthiae in the branchial sac, which is 

 not plicated ; their envelope is gelatinous ; 



3d. The CLAVELLIN^E, whose branchial sac is without plicae, and does not pene- 

 trate to the bottom of the envelope, and whose body is supported by a pedicle ; their 

 envelope is gelatinous ; 



4th. The BOLTENIA, whose body is pediculate, and the envelope coriaceous. 



He also takes into consideration the number and form of the tentacula which 

 internally surrouud the branchial orifice, but these characters, which are partly 

 anatomical, cannot be applied with certainty to a great number of species. 



M. Maclcay (Lin. Trans., XIV, part III) establishes two more, CYSTINGIA and 

 DEXDRODOA, founded on similar characters. 



* Ascidia pedunculata, Edw., 356 ; and Asc. clavata, or Vorticdla Boltenii, Gm. 



f. It is to M. de Savigny that we are indebted for our recent knowledge of the 

 singular organization of the whole of this family, formerly confounded with the 

 Zoophytes, properly so called. At the same time, Messrs. Desmarets and Lesueur, 

 made known the particular structure of the BotryUi and Pyrosomte. See the ex- 

 cellent work of M. Savigny in his Mem. sur les anim. sans, verteb,, part II, fasc. T. 



