No. 3.] BUDDING IN PEROPHORA. 391 
differently in different ascidians, still, in the buds of one and 
the same form statements of authors are at variance. 
Seeliger (29) describes the pericardium as arising in the buds 
of Clavelina from an enormously large evagination of the ven- 
tral portion of the branchial sac, which later becomes separated 
as an independent vesicle. He did not, however, distinguish 
the epicardial sacs, and mistook a part of the latter for the peri- 
cardium. Van Beneden and Julin (33) showed conclusively 
that the diverticulum of the branchial sac, observed by Seeliger 
and called by him the pericardium, is merely a part of the 
stolonic partition wall and is not concerned in the formation of 
the heart. According to the Belgian authors, who described 
in detail the development of the pericardium in the buds of 
Clavelina, the pericardium and epicardium at first form a com- 
mon cavity with the inner vesicle. A separation takes place 
later in such a way that the epicardium remains in communica- 
tion with the inner vesicle, while the pericardium becomes 
entirely cut off from the latter, but retains its connection with 
the stolonic partition. Van Beneden and Julin maintain that 
the union of the epicardium with the branchial sac is never lost 
in the bud development of Clavelina, and, therefore, do not 
agree with Seeliger’s statement that the diverticulum, which 
he observed and erroneously regarded as the pericardium, 
becomes separated from the branchial sac. Seeliger’s descrip- 
tion of the early constriction of the inner vesicle from the 
stolonic partition is not confirmed by the Belgians, who showed 
that the pericardium, originally a part of the inner vesicle, 
preserves its connection with the partition wall, as explained 
above. 
A somewhat similar origin of the pericardium, together with 
the epicardium from the inner vesicle, is stated by Pizon (22) 
to occur in the Polyclinidae; for example, in Circinalium and 
Amaroucium. 
Our knowledge of the derivation of this structure in the buds 
of Botryllus is very much less certain. Pizon (22) declares that 
the pericardium arises as a little diverticulum from the lower 
wall of the inner vesicle, which becomes completely constricted 
off as an elongated tube. His conclusion as to the endodermal 
