No.1.] BUDDING IN GOODSIRIA AND PEROPHORA. 169 
branchial sac. One or two sections farther back this cavity 
disappears, and to the very last is wholly shut off from the 
large single surrounding cavity marked a7. The section shown 
in Fig. 31 is thirteen sections farther back than the one shown 
in Fig. 30. 
It thus appears that while the peribranchial sacs become 
wholly separated from the branchial sac, they do not become 
separated from each other, but remain in very wide communi- 
cation, this communication occurring both behind the posterior 
extremity of the branchial sac and over its dorsal part. (Com- 
pare Fig. 31.) It is this common cavity into which the two 
peribranchial sacs open, and which may be regarded as an 
unmodified remnant of the primitive inner vesicle that has 
been called the cloaca ; but it is important to recognize that in 
this species, as in many others, it is neither morphologically 
nor physiologically wholly distinct from the peribranchial sacs. 
By this time numerous branchial stigmata have formed, par- 
ticularly in the anterior portion of the branchial sac. The 
peripharyngeal band and the branchial tentacles are already 
partly developed, and the dorsal lamina, @/, Fig. 30, has 
become quite a conspicuous object on the sections, though it 
has not yet become rolled over at its edge as it always appears 
in the adult (Fig. 6, Pl. XII). The endostyle is also distinctly 
marked out, though it is not histologically fully differentiated, 
(end., Fig. 30). Likewise the internal longitudinal bars (2.2.0., 
I, 2.26., 2, etc., Fig. 6) have begun to form. 
The formation of the branchial and atrial openings seems 
deserving of a little special attention. The development is 
initiated by an evagination from the inner sac, for each orifice 
(Fig. 35, a¢.szp., Pl. XIV). A little later an invagination forms 
immediately over this in the ectoderm ; the two meet, fuse, the 
fused wall becomes broken down, and by gradual but later- 
accomplished perforation of the overlying test, communication 
is established between the outside world and the respective 
sacs (Fig. 36, Pl. XV). The fact to which I wish to call atten- 
tion appears in the course of later development. It is illus- 
trated by Fig. 36, drawn from a section through a branchial 
siphon in which the opening is completed so far as the cellular 
