92 
ANNIE MATTHEWS. 
the early round planula stage. A definite membrane is now present 
between the ectoderm and the endoderm. X 78. 
Fig. 17. — Sagittal section of smooth oval planula, with broadened 
anterior end. Endoderm cells in places only one row deep, but in 
others form club-like processes. (Second free-swimming day.) x 133. 
Fig. 18. — Ectoderm and endoderm cells from a somewhat younger 
pre-planula than PI. 3, fig. 14, and at a later stage than Text-fig. 2. 
Yolk globules fewer than in early pre-planula and increasing in size. 
X 760. 
Fig. 19. — Part of a vertical section of a young polyp with mesenteries 
and spicules. One mesentery is cut through vertically near its attach- 
ment to the lateral wall. Many scleroblasts and nematocysts are 
thus cut across, which have been drawn into the mesoglcea of the 
mesentery here. At the lower right-hand corner young scleroblasts 
and nematocyst cells are shown in situ at the base of the columnar 
ectoderm, x 380. 
Fig. 20. — Ectoderm and endoderm cells from a late morula stage, 
x 133. 
Fig. 21. — Transverse section of an earlier morula stage than fig. 20, 
showing large yolk globules in the endoderm and smaller ones in the 
cuboid ectoderm. X 167. 
Fig. 22. — Nematocysts (oval bodies of Hickson), from mesoglcea of 
solitary and colonial polyps. 
PLATE 4. 
Fig. 23. — Sagittal section of a polyp about stage shown in fig. 3. 
This section does not cut through the mesenteries. X 133. 
Fig. 24. — Sagittal section of newly-fixed larva, still planula-shaped 
and ciliate. At the base the outer edge of the ectoderm has been 
diagrammatically thickened in the drawing, to indicate clearly the 
extent of the fixed area. X 133. 
Fig. 25. — Vertical section of polyp with only one pinnule on tentacles, 
i.e. about six days fixed. At Mes 2 and Mes 4 the basal attachments 
of the two lateral mesenteries Mes 3 and Mes d are seen. At V. 31. F x 
is shown the termination of the ectodermic outgrowth forming the 
mesenteric filament of mesentery 31es 3 , i.e. about half way down the 
free edge of the mesentery. At S. 0. the continuity of the stomodaBum 
and this outgrowth is shown. X 133. 
Fig. 26. — Vertical section of a polyp fixed from six to seven days, 
showing the strap-like ectodermic process on the right, which forms 
the ventral mesenteric filament, and on the left the shorter ectodermic 
