ON THE PERIVISCEEAL CAVITY OF OIONA. 119 



On the Perivisceral Cavity of Ciona. 

 By 



A. H. L.. IVcwstead, B.A., 



Late Scholar of Christ's College, Cambridge. 



With Plate 8. 



The genus Ciona differs from other simple Ascidians in 

 having the alimentary canal (except the rectum) and other 

 organs contained in a definite cavity, which is situated in the 

 region of the body posterior to the pharynx — the so-called 

 '^body-cavity" of Ciona. From its position round the viscera 

 this cavity may be called the perivisceral cavity, which implies 

 nothing as to its nature, while the term body-cavity might be 

 taken to assume its coelomic nature as definitely known. 



This investigation had for its object the determination of 

 the exact nature of this cavity, and was carried on partly at 

 the Zoological Station of Naples during the summer of 1891, 

 and since then at Cambridge. 



A. Previous Researches. 



The existence of this cavity was first made known by 

 Kupffer,^ who described it as a coelom or body- cavity. It is 

 separated from the atrial cavity by a septum which is per- 

 forated by the oesophagus, rectum, and genital ducts. In this 



* I take the account of Kupffer's work from the paper of vau Beneden and 

 Julin (2, p. 430). I regret that I have been unable to refer to KupfFer'a 

 original paper. 



