No. 3.] BUDDING IN PEROPHORA. 277 
and median portions of the peribranchial cavity in this ascidian 
arise at the same time as a saddle-shaped bag, which is cut off 
by two longitudinal furrows from a median vesicle, the later 
branchial sac. Hjort regards this process as a great curtailing 
of the embryonic development, such as often takes place in 
buds. Salensky (27) confirms this conclusion, but goes a step 
further, saying that “die Entwicklung der Peribranchialhohlen 
des Botryllus eine Abkiirzung nicht nur beziiglich der embry- 
onalen Entwicklung, sondern auch beziiglich der Entwicklung 
dieser Organe in den Knospen anderer Ascidien darstellt,”’ 
Distaplia, for example. My observations on the development 
of this structure in Pevophora viridis, although agreeing with 
those of Hjort in so far as they show that the peribranchial 
sacs do not arise separately as closed vesicles which later unite 
to form the cloacal cavity, indicate that the process is not so 
simple as that which occurs in Botryllus. 
If a transverse section of a bud be examined about the time 
when the elongation spoken of above is just beginning, it will 
be found that the wall of the inner or endodermal vesicle is no 
longer of uniform thickness. Pl. XXX, Fig. 9, is drawn from 
such a section. The ectoderm covering the bud, although it is 
not shown in the figure, has again become flattened after its 
temporary thickening, and is now like that of the stolon. The 
figure clearly shows that the stolonic partition is made up of 
two lamellae, which are continuous below with each other and 
pass over above into the walls of the inner vesicle. 
The important change to be noted, however, is that the wall 
of the endodermal vesicle on one side, the left, is getting per- 
ceptibly thinner than elsewhere, and that the whole vesicle is 
no longer symmetrically placed with reference to the stolonic 
partition, but is bulging out slightly to the right. This is the 
first indication of a marked change which is about to take place 
in the internal relations of the bud-rudiment. 
By a peculiar process, which may be described as a transverse 
or rotatory growth affecting the inner vesicle, the thicker wall 
of the right side (Fig. 9, 7.w.2z.v.) is carried or pushed down 
gradually until it comes to lie eventually on the ventral side, 
that is, the side next to the stolon. 
