No. 3.] BUDDING IN PEROPHORA. 383 
been referred to. By this time the process of displacement is 
completed, and the definitive symmetrical arrangement of the 
pharynx and peribranchial cavity is reached. The connection 
between the left peribranchial sac and the partition of the 
stolon is nearly severed; it is found in only two sections of this 
series, one of which is seen in Fig. 24. A total preparation of 
a bud at about this stage is shown in Pl. XXIX, Fig. 5, which 
may be readily compared with these sections. 
Epicardium. 
This structure was first described by Van Beneden and 
Julin (33) in the buds and larvae of Clavelina, and was 
shown by these authors to be closely connected with the 
development of the pericardium. It arises as an evagination of 
the posterior wall of the branchial sac, and a little further back 
divides into two blind pouches, which remain separate in the 
buds, but in the embryo unite to form the “cul de sac epicar- 
dique’’ of Van Beneden and Julin; the latter is continued into 
the stolon to form the double-walled partition. The develop- 
ment of the epicardium will be again referred to in connection 
with the pericardium, with which it stands in very close relation 
in some ascidians. 
In Distaplia, Salensky (27) has described the epicardial sacs 
as arising in the buds at an early stage by evagination from the 
posterior end of the inner vesicle; the two sacs are not formed 
at the same time, and the left one is always larger than the 
right. 
In the buds of the Polyclinidae the epicardium is formed in 
the same way; two small diverticula, a right and a left one, are 
given off from the posterior end of the branchial sac, from 
which they afterwards become detached. They soon, however, 
unite to form a single tube, which is continued out into the 
post-abdomen, where it is destined to furnish the inner vesicles 
of the buds produced by transverse constriction of that region 
of the body. 
The existence of an epicardium in Botryllus is denied by 
Hjort (8), but maintained by Pizon (22). According to the 
