42 SIDNEY P. HABMER. 



Fig. i. — C. eburnea. Spermatozoa. To tlie right, three mature sperma- 

 tozoa, drawn in the living condition (Zeiss, E) ; to the left, three stages in the 

 development of the spermatozoa, treated with osmie acid and picro-carmine 

 (Zeiss, F) ; in the middle, four immature groups consisting of four spermatozoa 

 each, killed with osmic vapour (Zeiss, -^ immersion, 4 oc). 

 Figs. 5— 7.— C. ramosa (Zeiss, DD). 



Fig. 5. (Combined from several sections of the same ovicell.) The egg 

 has divided into three blastomeres ; the valve is developing, and the 

 distal end of the tentacle-sheath has become thickened. 

 Fig. 6. Proximal end of a longitudinal section (more advanced). The 

 embryo consists of a compact rounded mass lying iu a large follicle, 

 which projects freely into the tentacle-sheatli. 

 Fig. 7. A similar preparation at a stage when the vacuolation of the 

 follicle is commencing. 



PLATE II. 



Fig. 8. — Crisia eburnea. Ovicell at a stage corresponding to Fig. 6 in C. 

 ramosa. The embryo is larger and the follicle is much smaller than in that 

 species (Zeiss, DD). 

 Figs. 9 — H. — C. ramosa (Zeiss, D D). 



Fig. 9. The vacuolation of the follicle is nearly complete. The tubular 

 aperture is formed, and the structures connected with its base are well 

 developed. 



Fig. 10. Invagination (?) in a " primary embryo," at about the same 

 stage as Fig. 9. 



Fig. 11. Considerably later stage. The follicle lias become a dense 

 protoplasmic reticulum, containing the massive " primary embryo," now 

 transformed into a budding organ, which is giving rise to numerous 

 secondary embryos, three of which are seen lying freely in the reticu- 

 lum. At the upper end a giant-cell, derived from the thickened distal 

 end of the tentacle-sheath (cf. Figs. 5, 13 and 9). 



Figs. 12 — 14. Illustrating the development of the aperture of the ovi- 

 cell. In Fig. 12, the primary aperture still remains open, the distal 

 end of the tentacle-sheath being thickened. In Fig. 13, the tubular 

 aperture of the adult ovicell is developing; it contains the remains of 

 the primary aperture. The thickening of the distal end of the tentacle- 

 sheath has increased in size, and the valve is well developed. In Fig. 

 14, the tubular aperture is almost complete. The thickening of the 

 tentacle-sheath still extends into its base. At its distal end a de- 

 pression occurs, which is possibly the remains of the primary aperture. 

 The tube ends in a cap prolonged into a narrow tube, of unknown 

 significance. 



