ACEPHALA NUDA. 429 



ceral mass. The envelope is much larger than the mouth, which is 

 fibrous and vascular, and on which, between the two tubes, is one of 

 the ganglions. These animals attach themselves to rocks and other 

 bodies, and are deprived of all power of locomotion; the chief sign 

 of vitality which they exhibit, consists in the absorption and evacu- 

 ation of water through one of their orifiices; when alarmed they eject 

 it to a considerable distance. They abound in every sea, and some 

 of them are eaten(l). 



Some species are remarkable for the long pedicle which supports 



theni(2). 



FAMILY II. 

 AGGREGATA. 



The second family consists of animals more or less analogous 

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

 seem to communicate organically with each other, and in this 

 respect to connect the Mollusca with the Zoophytes ; but in- 

 dependently of their peculiar organization, these animals, ac- 

 cording to the observations of Messrs Audouin and Milne Ed- 



(1) The whole g-enus Ascidia, Gm., to which must be added the Asc. gelatinosa, 

 Zool. Dan., sliii; ^sc. pyriformis, lb., clvl; Salpasipho^ Forsk., xliii, C; Ascidia 

 microsma, Redi, Opusc, III, Pi., App., Vll, the same as the Asc. sulcata, Coque- 

 bert. Bullet, des Sc. Avril, 1797, I, \;Asc. glandiformis,Co(i\xe.h.,\h. N.B. 

 The Ascidia canina, Mull, Zool. Dan., Iv, J.sc. intestinalis, 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, siich as,, 



1st. The Cynthi.e, whose body is sessile and branchial sac longitudinally pli- 

 catedi their envelope is coriaceous; 



2d. Tlie Phallusije, which differ from the Cynthise in the branchial sac which is 

 not p]icated;their envelope is gelatinous; 



3d. The Ct.AVELi.ix;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 Bolteni^, whose body is pediculate, and the envelope coriaceous. 



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

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

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



M. Macleay (Lin. Trans., XIV, part III) estabUshes two more, Cystixgia and 

 Dendrodoa, founded on similar characters. 



(2) Ascidia peduncukda, Edw., 356; and Asc. clavata, or Vorticella Boltenii, Gm. 



