THE DEVELOPMENT OF ALCYON1UM DIGITATUM. 
91 
PLATE 3. 
Fig. 1. — Sagittal section of long highly contractile planula, towards 
end of free- swimming life. Yolky detritus still present in coelenteron. 
Ectoderm very full of mucous cells and nematocysts. X 78. 
Fig. 2. — Portion of ectoderm of full-grown planula, showing mucous 
cells and nematocysts among the ordinary cells. Granular reticulate 
protoplasm in mucous cells very deeply stained, x 507. 
Fig. 3. — Lateral view of polyp with older mesenteries than fig. 4. 
Second day of fixation. Adhesive plug shows well. X 16. 
Fig. 4. — Lateral view of polyp during early part of second day of 
attachment. Eight mesenteries appearing, x 16. 
Fig. 5. — Lateral view of polyp on the fifth day of attachment. 
Tentacles partly contracted, body expanded. X 37. 
Fig. 6. — Oral view of young polyp, with tentacles well expanded and 
mouth widely opened. The tentacles were still reddish-yellow and the 
body wall cream ; spicules abundant (about five days fixed). X 35. 
Fig. 7. — Oral view of polyp about the sixth day. Tentacles partly 
contracted, but mouth still exposed, x 39. 
Fig. 8. — Section through the eight-lobed egg of Text-fig. 30. X 78. 
Fig. 9. — Sagittal section through eight cell stage. One of the several 
nuclei that have again divided ready for the next segmentation is 
shown at N. X 78. 
Fig. 10. — Section through an egg protruding sixteen lobes ; two 
daughter nuclei are drawn, x 78. 
Fig. 11. — Sagittal section through sixteen cell stage, showing de- 
lamination spindle. X 78. 
Fig. 12. — Transverse section of a young morula showing delamination 
and ordinary spindles. X 78. 
Fig. 13. — Enlarged drawing of section of two blastomeres from the 
sixteen cell stage. The finely granular outer area, and large and small 
yolk globules are shown, x 133. 
Fig. 14. — Five endoderm cells from a late pre-planula, in which the 
lobes are almost withdrawn again. The yolk globules are few and very 
large and the segmentation cavity has disappeared. X 760. 
Fig. 15. — Ectoderm and endoderm cells from transverse section of a 
late pre-planula, when the ectoderm cells have become much longer 
nd narrower, while large vacuoles are still present. X 78. 
Fig. 16. Transverse section of a very late pre-planula, with rapidly 
proliferating ectoderm (stage of Text-fig. 3), just before it passes into 
