No. 3.] BUDDING IN PEROPHORA. 379 
further down on the left side; but that the anterior end is 
slightly rotated is shown by the fact that the rudiment appears 
not exactly in the median line, where it is eventually brought 
through the shifting of the vesicle, but somewhat to the /eft 
of it. 
The formation of the peribranchial cavity is associated with 
this change of position of the endodermal vesicle. In Figs. 10 
and II it is seen that the lower portion of the vesicle at the 
point indicated by the line @ is being bent in, with the result 
that the wall in this region makes two angles, one directed 
inward and the other outward (Fig. 11,,@a and 4). The apex of 
the latter marks a point on the wall of the vesicle which will 
have traveled through 90° when the displacement is completed, 
as its final position will be in the mid-ventral line. 
As the inwardly directed fold (Fig. 11, f/.40.s.) deepens, it 
gradually divides off a portion of the inner vesicle on the left 
side, which is connected with the stolonic partition; this is the 
left peribranchial sac (Pl. XX XI, Fig. 20, /.por.s.). This fold 
begins somewhat in front of the middle of the vesicle, and, 
deepening rapidly in this region, gradually extends posteriorly. 
As these changes are going on, the connection with the 
stolonic partition is gradually becoming constricted, and is now 
only present in the posterior half of the bud, while at the same 
time the-ectodermal stalk is also getting narrower. Ritter (24) 
in a preliminary note on the budding of Perophora says that 
“when the differentiation of the ‘endoderm’ into the branchial 
and two peribranchial sacs takes place, it does so in such a way 
that the developing blastozodid is connected with the double- 
walled partition of the stolon, not by the branchial sac, as has 
been hitherto supposed, but by the left peribranchial sac.’’ He 
does not, however, describe how this comes about. From an 
examination of Pl. XXX, Figs. 9, 10, and I1, it is readily 
understood. The communication of the body cavity of the bud 
with the blood spaces of the stolon is never completely closed, 
as there is always a free circulation of blood from the one to 
the other; but eventually the left peribranchial sac is entirely 
severed from the stolonic partition. I cannot, however, con- 
firm Ritter’s statement (doc. ci¢., p. 367) that this connection is 
