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PLATE X.

PALUDICELLA EHRENBERGI.

Fig.

1. Paludicella Ehrenbergi, attached to a submerged stone. Natural size.

2. A portion of the same magnified.

3. A very much enlarged drawing of a cell with the polypide retracted; showing the anatomical details.

4. A cell seen in section with the polypide exserted, and exhibiting anatomical details. The ovary and testis are here fully developed, while in fig. 3 they are represented in an undeveloped state.

5. Lophophore viewed upon the upper surface, with the mouth, and roots of the tentacula.

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PLATE XI.

DEVELOPMENT of GEMMA AND Ovu M.

Fig. 1–9. Successive stages of the development of the gemma in Paludicella Ehrenbergi. 10–16. Successive stages of the development of the gemma in Lophopus crystallinus. 17. Cell from the testicle of Alcyonella fun/osa filled with secondary nucleated cells (“vesicles of evolution”). 18. The mother-cell has disappeared, but the vesicles of evolution still adhere together, while from several the spermatozoal filament is seen projecting. 19. A mother-cell containing vesicles of evolution; the spermatozoal filament has become partially liberated from several of the vesicles of evolution, and appears to perforate the walls of the mother-cell. 20. A vesicle of evolution more highly magnified. The original nucleus has become converted into a spermatozoal filament, which lies coiled up within the cell. 21. Spermatozoal filaments escaping from the vesicles of evolution. 22. A vesicle of evolution with the spermatozoal filament partly liberated, and presenting a spiral form. 23. Spermatozoa of Alcyonella fungosa as they appear when floating freely in the fluid of the perigastric space. 24. Mother-cells containing nucleated vesicles of evolution from the testis of Paludice/a Ehrenber/i. 25. Free spermatozoa of Paludicella Ehrenbergi. 26. A group of ova from the ovary of Alcyonella fun/osa. 27. A single ovum from the same, more highly magnified. 28. The ovum has undergone segmentation, and a central cavity has begun to show itself. 29. The embryo is here seen in the form of an oval ciliated sac, destitute as yet of external orifice. 30. The embryo now presents an orifice through which an unciliated portion is protruded by a process of evagination. In this protrusible portion a polypide is developed. 30". The polypide from the last isolated. The lophophore is as yet destitute of tentacles. 30". The same polypide slightly more advanced. Some tentacles have begun to develope themselves from the margin of the lophophore. 31. An embryo containing two polypides. 32. The same more advanced. The polypides have acquired nearly their perfect development. .33. The same, with the anterior part withdrawn into the posterior, as occurs when the embryo is in the act of swimming. 33". A group of embryos in this stage of their natural size. 33". A similar group more magnified, and in the act of swimming. 34. More advanced stage. The first invagination has become obliterated; the cilia have disappeared from the surface, and the young polyzoon has acquired its ectocystal

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