ACTINIAN BDNODEOPSIS GLOBULIFERA. 307 



comjiaratively long, extending into the gastro-coelomic cavity for nearly one-half the 

 height of the polyp, its inner free mjirgin heing reflected (PL 25. fig. l). The ectoderm 

 is often thrown into vertical folds, which are without any regular disposition, not 

 necessarily corresponding with the mesenteries. The layer exhibits the same structure 

 all the way round, being in no way modified to form special gonidial grooves opposite 

 the directives. Prof. Verrill, in his description of the external characters of the Bermudas 

 specimens, mentions the occurreuce of gouidial grooves, but such are certainly not 

 indicated in the histology of the stomodseiim of the Jamaica representatives, and were 

 not recognizable in the living polyps. h\ other species of Actiniae where gonidial grooves 

 occur, the ectoderm lining them usually offers a n)arked contrast with that along the 

 lateral walls ; the cilia are more strongly developed, and fewer gland-cells and neuiato- 

 cysts occur than elsewhere. 



The stomodseal ectoderm {ecL, PL 25. tig. 7) is strongly and uniformly ciliated all 

 rorxnd, and contains nematocysts [item.) and granular gland-cells. The former are sparse 

 towards the upjjer extremity, but as the lower free end is approached they become very 

 numerous, and are all of the thick-walled variety, such as occur in the columnar 

 evaginatious, but slightly smaller, measuring -0:^5 mm. in length. In the inner part of 

 the layer they are irregularly arranged at all angles with the free edge, but towards 

 the surface they become parallel with the other constituents. The ectodermal muscle 

 (ect.tn.) and ganglion-layer {/tr.l.} are only feebly developed. 



The mesogloea is extremely delicate throughout, and remains smooth on both sides. 

 The endoderm closely resembles that lining the coelomic cavity generally, and contains a 

 few Zooxanthellge in some places, while in others they are absent, in which latter case the 

 epithelium is very narrow. The circular endodermal musculature is recognizable in 

 vertical sections. 



Intermesenterially the stomodieum narrows gradually towards its free lower extremity 

 and becomes reflected, as on the left side of tig. i ; mesenterially the ectoderm appears 

 continuous with the iilament at the free edge of the perfect mesenteries. The stomodieal 

 waU on the right side of fig. J? terminates in a section of a mesenterial filament. 



3Iesentei'ies. 



The mesenteries are very varial)le in number in the many polyps examined, and 

 also in their cyclic relationships ; for a long time it seemed impossible to establish 

 any hexameral or other regular system of arrangement. The conditions encountered 

 will be best understood by reference to PL 26. figs. 9 to 15, representing outline 

 sections through the stomodaeal region of six different polyps. 



In fig. 9 only three pairs of complete mesenteries occur, and two pairs which are 

 incomplete. The lower comjilete pair (d.) are directive mesenteries, having the 

 longitudinal muscle on the faces looking away from one another. The polyp from 

 which fig. 10 was taken possessed three pairs of complete mesenteries, including a 

 pair of directives and a single member of another complete pair. Within the wide 

 interval on the right side are nine, short, incomplete mesenteries, which present some 



45* 



