PLATE XI. 



Development of Gemma and Ovum. 



Fig. 



1 — 9. Successive stages of the development of the gemma in Paluclicella Ehrenhergi. 

 10 — 16. Successive stages of the development of the gemma in Lophopus ci-ysfaUinHS. 



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 Alcgonella 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 Paliidicella 



Ehrenhergi. 



25. Free spermatozoa of Paluclicella Ehrenhergi. 



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- 



ment. 



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 The same, with the anterior part withdrawn into the posterior, as occurs when the 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 



