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DEVELOPMENT OF GEMMA AND OVUM.
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 fungosa 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 Paludicella Ehrenbergi.
25. Free spermatozoa of Paludicella Ehrenbergi.
26. A group of ova from the ovary of Alcyonella fungosa.
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 develop
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 The same, with the anterior part withdrawn into the posterior, as occurs when the embryo is in the act of swimming.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
PLATE XI (continued).
investment. A new bud is seen at each side within the cell, near its anterior extremity.
35. Embryo of Plumatella fruticosa.
36. Statoblast of Lophopus crystallinus in a very early stage, in which it appears as a minute swelling upon the funiculus.
37. The same more advanced. The contents of the statoblast are here seen to be divided
into two distinct portions.
38. The same still further advanced. The division into two masses has disappeared, and the whole contents are surrounded by a distinctly cellular membrane.
39. The same after the appearance of the annulus, which as yet presents but a simply granular structure.
40. Peculiar cells from the annulus in a later stage of development.
41. The statoblast ruptured under compression, and the contents escaping in the form of minute cells.
41. A group of cells constituting the contents of the statoblast, more highly magnified. 41. Peculiar refractive corpuscles constituting the contents of these cells.
42. Statoblast of Plumatella repens, with the young polyzoon escaping from it.
Its two faces have separated from one another, and are seen still adhering to the posterior part of the polyzoon which floats freely through the surrounding water. The polypide is here represented as exserted from its cell.
43. The same, with the polypide retracted.