ACTINIAN BUNODEOPSIS GLOBULIFERA. 305 



The longitudinal ectodermal muscle is supported upon the mesogla3a, which is usually- 

 thrown into slight folds to give it increased area, especially towards the proximal end. 

 The nerve-ganglion layer is also clearly developed. 



The endodermal epithelium is rather broad in the partly retracted tentacles, and 

 exhibits an irregular free surface, while Zooxanthelhc are only sparsely distributed. 

 The endodermal muscle (end.m., fig. 3) is comparatively well developed, the mesogkea 

 presenting delicate plaits for its support, best seen just above the tentacular 

 septum (i.c.s.). 



The tentacular cavity is separated from the general polypal cavity by a circular 

 transverse partition, perforated iu the middle, and situated a very short distance from the 

 origin of the tentacles (tigs. 3, 4, (5). The septum is covered on both sides by endoderm, 

 and the supporting mesogloea is narrow and lined by delicate muscle-libres on its 

 inner and outer surfaces, continuous with the circular musculature of the tentacles. Its 

 central free margin is thickened, and the mesoglcea becomes plaited {t.sph., tigs. 3 &6) in 

 a sub-dendroid manner to afford additional support for the muscle-tibres, which here 

 constitute a circular sphincter muscle. Various appearances of the partition in section, 

 showing its relation to the coeloraic and tentacular cavities, are indicated in figs. 4 and 13, 

 and the sphincter muscle {t.sph.), more highly magnified, iu PL 25. figs. 3aud 0. Where 

 in fig. 13 the section includes the middle of the partition the two free edges are seen to be 

 in the main directed downwards into the polypal cavity, so that the membrane must be 

 concave on its tentacular aspect and convex on its ccelomic side. In fig 13, tentacles 

 ^1, ('2, and ^10 are partly constricted at their origin, and such a condition has been noted 

 among the external characters (fig. 1 c). No doubt the constriction is brought about by 

 the action of the sphincter. In fig. 3 the tentacular wall immediately below the 

 partition is seen to have become much thinned. 



The presence of a tentaculo-coelomic septum and sphincter has already been recognized 

 in the genus Bolocera, including also the genus Boloceroides of Carlgren (1899, p. 43; 

 1900, p. 15). Carlgren (1893) descri!)es and figures the formation at the base of the 

 tentacles in Bolocera loiigiconiis, and the musculature is there not much better develojjed 

 than in Buiiodcopsis. In Bolocera the contraction of the sphincter often leads to the 

 detachment of the tentacles from the disc. In one or two of the Jamaica specimens of 

 Btmodeopsis glohuUfera circular apertures occur in the tentacular zone, indicating that 

 tentacles have disappeared therefrom, but I have never actually observed the j)rocess 

 taking place in the living polyp. In B. antllUensis, however, the tentacles were found 

 to be readily detached on handling the polyps, and in this species also a tentacular 

 septum and sphincter occur. Carlgren has pointed out that the partition comes off along 

 with the tentacles, and such would certainly be presumed from the great narrowing 

 which takes place immediately below the membrane, as represented in fig. 3. 



McMurrich (1893, p. 154, pi. xxii. fig. 27) also describes and figures the tentacular 

 sphincter iu Bolocera occidua. In many of his sj)ecimens, mesenterial filaments were 

 lound protruding from the openings at the margin of the disc formed by the falling off 

 of the tentacles. The same author includes the deciduous character of the tentacles 



SECOND SERIES. — ZOOLOGY, VOL. VIII. 45 



