14 



THE ANTHOZOA 



mesenteries are formed as eight radial folds of the endoderm, 

 which arise simultaneously at the oral end of the embryo at the 

 time of the formation of the stomodieal invagination. The tentacles 

 are formed as eight outgrowths surrounding the mouth, simple at 

 first, but soon acquiring lateral pinnules. The embryo is now a 

 zooid, and after a period of growth it gives oflF solenia, and from 

 these buds are produced, or in more differentiated colonies an 

 axis and other structures characteristic of particular groups are 



^ m.9Mm. 



Fio. V. 



Developmental phases of Gorgonia Cavolinii, after G. von Koch. 1. A mature ovimi. 2-4 

 Progressive stages of segmentation. 5. Section through a mature and an immature ovum in 

 their follicles, en, endoderm ; mg, mesogloea. (5. Section of an embryo of the .same stage as 4. 

 7. Section of a later stage showing the commencing disintegration of the central cells of the 

 endoderm, and the columnar ectodenn. S, 9, and 10. Planulae in different stages of contrac- 

 tion. 11. A larva \iewed from the oral surface to show the Hrst traces of the mesenteries. 

 12. Tlie same viewed from the side. 13. Longitudinal section through a planula of about the 

 same stage as S, showing the coelenteron, nvl, the endoiienn, tn, and the ectodenn, ec. 14. 

 A young zooid with simple tentacles. 15. Vertical section of a free larva with stomoda-al 

 invagination. 10. Vertical section of an older fixed lana showing stomodaeum, st, opening 

 into the coelenteron. 17. A young zooid with pinnate tentacles. 



developed in connection with it. The development of the meso- 

 gloea has been most carefully studied in Eenilla by Wilson (96). 

 In an embryo of eight hours there is a delicate membrane lying 

 between the ectoderm and endoderm, on which the ectoderm cells 

 are planted, as on a basement membrane. This is the first sign 

 of the mesogloea, but the bulk of it is formed at a later stage by 

 deliquescence of the lower ends of the ectoderm cells and their 

 conversion into a gelatinoid substance. Spicules are formed in 

 rounded interstitial cells, which in the embryo occupy the deeper 



