384 LEFEVRE. [VoL. XIV. 
latter, the inner vesicle at a very early stage gives off two 
anterior lateral diverticula, one on each side, which later form 
the peribranchial cavity and also two posterior lateral diverti- 
cula. These four pouches are at first separate, but soon the 
two on each side fuse in the middle region of the bud. When 
the peribranchial cavity is separated from the inner vesicle, the 
posterior diverticula are cut off at the same time, and now 
appear as posterior prolongations of this cavity, with which 
they always remain in free communication. They are what 
Pizon calls the “ dverticules périviscéraux,” and in later stages 
completely envelop the digestive tract. From the fact that 
these pouches arise as two diverticula from the posterior end 
of the inner vesicle, Pizon regards them as homologous with the 
epicardial tubes of other ascidians, and states (loc. cit¢., p. 29) 
that ‘la formation de cette cavité périviscérale n’est pas secon- 
daire et qu’elle s’est annoncée, des le début, par deux petits 
diverticules postérieurs de la vésicule primitive, en mémetemps 
que les diverticules antérieurs correspondants qui engendreront 
la cavité péribranchiale.” 
These perivisceral diverticula, however, differ from the epi- 
cardial tubes of Clavelina, Distaplia, and the Polyclinidae in 
that they communicate with the peribranchial cavity. 
Hjort (loc. czz., p. 594) states that the “einheitliche Peri- 
branchialblase sich nun derart weiter entwickelt, dass sie nicht 
nur den Abschnitt des Kiemendarmes, sondern den ganzen 
Darmtractus unwachst,” and Salensky (27), who accepts the 
conclusion of Pizon as to the homology of the perivisceral 
diverticula, thinks that Hjort evidently saw the “epicardial 
sacs’’ in Botryllus but failed to recognize them as such. 
Salensky believes that the connection of the “ epicardial sacs”’ 
with the cloaca in Botryllus must be regarded as a result of the 
early separation of the peribranchial cavity from the inner 
vesicle. 
In the light of these considerations it is possible that the 
posterior extensions of the peribranchial sacs, which I have 
described as arising in the buds of Pevophora viridis, are like- 
wise homologous with the epicardial sacs of other ascidians. It 
is to be remembered, however, that if such be the case, which 
