THE ANATOMY OE THE MADREPORARIA. 423 



(cf. p. 8, supra) are well developed, not only on the mesentery, 

 but also on the thickened mesogloea at the sides of the pseudo- 

 costse (v. infra, and figs. 10, 11, a). 



Encapsuled in the mesogloea lamina of the mesentery and of 

 its craspedon are numerous ova in various stages of matura- 

 tion. So far as I am aware, all Anthozoan ova as yet 

 described are formed in the endoderm, and then migrate 

 into the mesogloea, the latter forming a capsule appressed 

 closely round them. In Sphenotrochus, however, the ovum is 

 surrounded by a series of deeply staining bodies which lie 

 between its membrane and the mesoglceal capsule (fig. 12). 

 At first sight these corpuscles appear to consist of extruded 

 yolk, but in most, if not in all, it is possible to detect a faint 

 nucleus. Nearly triangular in section, their bases are pressed 

 closely against the capsule, from which they sometimes shrink 

 away, allowing their outline to be clearly seen. It is hardly 

 possible to regard them as other than follicular cells. They 

 are not present in the capsule of the smallest ovum observed 

 (•lx'07 mm., diam. nucleus '008 mm.), and their number 

 increases up to a certain point with the size of the ovum. It 

 is probable therefore that they migrate from time to time into 

 the mesogloea, as does the ovum itself; and their appearance 

 indicates that their function may be to supply yolk-material 

 for the ripening egg-cell. More deeply staining and larger 

 bodies of irregular outline are found scattered in the endoderm 

 of the craspedon, apparently identical with those described in 

 Euphyllia (Bourne, ' Quart. Journ. Micr. Sci./ xxviii, p. 31) ; 

 these may bear some relation to the follicle cells. 



The soft tissues external to the theca are also of some 

 interest. No peripheral lamellse of the mesenteries are recog- 

 nisable, but at the points where they might be expected to 

 occur are formed outgrowths of corallum comparable to those 

 in Amphihelia (v. p. 5, supra.), on which the body wall 

 rests (fig. 10, B. a.). The costse corresponding to the ento- 

 coelic septa come also into direct contact with the body-wall 

 (ibid., a 1 ), while those of the entocoelic septa are free. At a 

 lower level, however, both sets of costee regularly serve for the 



