440 
W. A. JIASWELL. 
Fig. ‘2. — Transverse section through uterine ovum of T. fasciata. 
passing through the unsegmented ovum. X 250. 
Fig. 3. — Section through an early lilastodenn in which three kinds of 
cells have become distinguishable. X 500. 
PLATE 24. 
Fig. 4. — Section through a later stage, with groups of larger, lighter, 
surrounded by smaller, more darkly stained, cells. X 50o. 
Fig. 5. — Section through a lilastoderm in which the first definite 
trace of the cavity has made its appearance. X 500. 
Fig. 0. — Later stage in the development of the cavity. X 500. 
Fig. 7. Longitudinal section through the entire egg, with a more 
advanced cavity. X 170. 
Fig. 8. — Portion of a longitudinal section of egg passing through the 
cavity, and cutting the blastoderm nearly transversely. X about 330. 
Fig. 9. — Similar section of a later stage with the brain more 
advanced. X about 330. 
Fig. 10. — Similar section, cutting the blastoderm nearly transversely, 
Imt with some oblicpiity, so that it passes through the brain and one 
excretory sac. X 330. 
Fig. 11. — Anterior part of a vertical longitudinal section, approxi- 
mately median, at a stage when the rudiments of the tentacles and eyes 
are appearing. X aljout 330. 
PLATE 25. 
Fig. 12. — Entire longitudinal and vertical section of embryo with 
the tentacles further developed than at the stage represented in fig. 11, 
and flexed backwards over the mouth. X about 130. 
Fig. 13. — Anterior part of a longitudinal and approximately median 
and vertical section of an emliryo with well-developed, ventrally flexed 
tentacles. I 
Fig. 14. — Transverse section through the blastoderm in the region 
behind the endocoele at a stage somewhat later than that represented in 
fig. 10, showing the posterior jjrolongation comprising the genital rudi- 
ment. X about 500. 
Figs. 15 and 10. — Successive sections of an embryo at an early stage 
in the formation of the endocade, showing an early phase in the history 
of the cells destined to form one of the excretory sacs. X about 500. 
