230 RITTER. 
EXPLANATION OF PLATE XIII. 
Fic. 12. Section of the budding zooid shown in Fig. 9, the section corre- 
sponding to the line 4.4.’ X 87. 
Fic. 13. From the same series as 12, but far enough posteriorward so that the 
inner layer of the bud is not continuous with the maternal endoderm. At ams. 
are seen two ampullae of the testicular vessels which are in close contact with the 
young bud, and the vessel, ec.ves., is still more closely pressed by the bud. X 2tIo. 
Fic. 14. Transverse section of a bud not yet separated from its parent. 
X 210. 
Fic. 15. Section of a zooid with a bud, éd., almost severed, there being only 
a remnant, ~c., of the connection between bud and parent. The bud is here 
entirely undifferentiated as to the organs of the future zooid. 
Fic. 16. Optical section of a young bud; the intestine, zz, is established, 
and the folds that will ultimately separate the peribranchial sacs from the 
branchial sac, are barely indicated at .£ The ganglio-hypophyseal evagination, 
hy.cl., is represented as projected on the plane of the section. In reality it 
would not be seen at the focus at which the rest of the bud is shown. The begin- 
nings of the two so-called epicardial pouches will be observed at Y. Seen from 
the dorsal side. X 87. 
Fic. 17. A bud somewhat more advanced in development than the preceding. 
The specimen was cleared in clove oil. It is seen from the dorsal side, but is 
slightly rotated to the right. The right partitioning fold, 2.f, is well seen. The 
distribution of the blood cells in the body space is shown. X 87. 
Fic. 18. A bud considerably more advanced than the last, the peribranchial 
sacs nearly complete. Seen fromthe dorsal side. Viewed as a transparent object, 
but not shown in optical section. X 87. 
Fic. 19. A still older bud, the differentiation of the organs almost complete. 
Method of treatment and view similar to the last three. X 87. 
Fics. 20 and 21. Sections of a bud in which the peribranchial sacs, 47.5.a., are 
barely begun. The sections are not quite at right angles to the antero-posterior 
axis of the bud, and as a consequence the sacs do not both appear on the same 
section. X 210. 
Fics. 22-24 (and 25, Pl. XIV). Four transverse sections of a bud about 
corresponding in its stage of development to the bud shown in Fig. 17. Fig. 22, 
the most anterior of the series, passes through the position at which the branchial 
siphon, ér.szf., is soon to form. By Fig. 23 it is seen that the folds which are to 
separate the branchial from the peribranchial sacs extend along the ventral as 
well as along the dorsal side of the primitive inner vesicle, vf anda. In the 
last of the four sections, Fig. 25, no trace of the folds appears. This section 
passes through the beginning of the atrial siphon, at.st#. X 210. 
