234 THE VOYAGE OF H.M.S. CHALLENGER. 



extending beyond the branchial sac posteriorly. In this section he placed the two species 

 Ascidia intestinalis, Linmeus, and Ascidia canina, 0. F. Midler. 



In 18 28, •Flerning(" British Animals," p. 468), adopting Savigny's term, founded the genus 

 Oiona, for the common British species Ciona intestinalis. For a considerable time, how- 

 ever, this name was not received, and we find in Forbes and Hanley's " British Mollusca" 

 (1853), the two species intestinalis and canina still retained in the genus Ascidia. 



Things remained in this condition till 1870, when Hancock (Ann. and Mag. of Nat. 

 Hist., ser. iv., vol. vi.) revived Ciona as a generic name, gave it a full and satisfactory 

 definition, and added a new species, Ciona fascicidaris. The name has since been used 

 by Kupffer, Heller, and Traustedt, and may now be considered as firmly established. 



The body in Ciona is always sessfle and attached, and is usually elongated antero- 

 posteriorly. The test is soft and almost gelatinous, being flaccid and transparent when 

 living. The musculature of the mantle is equally developed upon both sides of the body, 

 and is rather characteristic. A few strongly marked bundles — twelve to fourteen in Ciona 

 intestinalis — are found running longitudinally from the bases of the siphons at the anterior 

 end to the opposite extremity of the body. The other muscle bands, which are transverse 

 and obhcpie, are very much weaker and more irregularly arranged. On account of the 

 strength of the longitudinal bands, and the softness of the test, the body has very great 

 powers of contraction. 



The branchial sac is neither folded nor plicated when living and expanded, but usually 

 when a specimen, which has been put into alcohol living, and has contracted its whole 

 body forcibly, is examined, the branchial sac is found to be crumpled and corrugated, so 

 as to give very much the appearance of " minute plication." This is merely caused, how- 

 ever, by the pressure of the surrounding mantle, and when that has been removed the 

 sac may be spread out so as to assume more the look of its natural structure. 



The most characteristic features of Ciona are the dorsal lamina, which is in the form 

 of languets, like those of Corella, and the alimentary and genital viscera, which are situated 

 upon the left side of the branchial sac, as in Ascidia, but extend beyond it posteriorly, so 

 as to form a rudimentary abdomen. In this last character Ciona differs from both 

 Corella and Ascidia, and shows affinity with Ecteinascidia and some of the other 

 Clavelinidae. 



This genus contains only a small number of species. In addition to Ciona cam mi, 

 0. F. Midler, Ciona intestinalis, Linnpeus, and Ciona. fascicularis, Hancock, which 

 have been mentioned above, there remain the Ascidia corrugata of the " Zoologia Danica," 

 which is probably either Ciona canina or Ciona intestinalis, Alder's 1 Ascidia .pulchella, 

 which may possibly be merely a variety of Ciona intestinalis, and Verrill's 2 Ciona 



1 Observations on British Tunicata, Ann. and Mag. Nat. Hist. ser. iii., vol. xi., 1863. 



2 Description of some imperfectly known and new AscidianB from New England, Amer. Jourii. of Sci. and Arts, 

 ser. iii., vol. i., No. 2, 1871. 



