122 A. H. L. NEWSTEAD. 



open into the perivisceral cavity, as supposed by van Beneden 

 and Julin ? 



(ii) Is there any communication between the atrial cavity 

 and perivisceral cavity, as described by Kupffer, and denied by 

 Roule? 



These points I hnve tried to work out by means of sections 

 of small individuals, about 1 — 2 cm. in length; such indi- 

 viduals have completely undergone metamorphosis and acquired 

 the adult form. 



A transverse section of a small Ciona through the posterior 

 end of the pharynx between the end of the endostyle and the 

 oesophageal opening — i. e. through the posterior groove — is 

 drawn in fig. 1, and a portion of the same section, more 

 enlarged, in fig. 3. 



The perivisceral cavity {pv. c.) is separated from the atrial 

 cavity {at.) by the septum (5.), in which is seen a blood-vessel 

 on one side. Inside the perivisceral cavity is seen the peri- 

 cardium (pc), attached by its mesentery (m, fig. 2) on the one 

 hand to the base of the posterior groove {p. g.), and on the 

 other hand to the stomach [st.) ; at its attachment to the pos- 

 terior groove is a large vessel {v., fig. 2) running beneath the 

 groove. Inside the pericardium is the heart [h.], which is cut 

 twice owing to its peculiar V-shape ; each part is seen to be 

 attached to the wall of the pericardium. On each side of the 

 posterior groove of the pharynx is an opening (0.), by which 

 the perivisceral cavity communicates with the pharynx. These 

 two openings are situated, one on each side, between the pos- 

 terior groove and the edge of the septum which elsewhere is 

 attached to the base of the groove ; they may be traced only 

 through a few sections (12 — 15), and the left is distinctly 

 larger than the right. 



On working through a series of sections no communica- 

 tions between the perivisceral cavity and the atrial cavity can 

 be seen. 



The above section, shown in fig. I, then, shows that definite 

 communications between the pharynx and perivisceral cavity 

 do exist ; and, since these openings occur in the same position 



