Part [1.—Stichodactyline and Zoanthec. 177 
endodermal, circular muscle. Towards the proximal region of the column, these 
processes become more numerous and longer, being even longer than the 
mesogloea is broad. 
The endoderm is devoid of zooxanthelle, and such is the case throughout the 
polyp. For some distance from the mesoglcea it is constituted largely of delicate 
fibrils, while the protoplasmic contents are aggregated near the free, irregular 
border. A nervous layer is distinctly shown in places. 
Sections through the verrucee present no histological difference from the rest 
of the column-wall, except that all three layers are thinner and the musculature is 
weaker. It is doubtful as to how far they can be compared with the verruce in 
the species already described. They certainly possess no adhesive power. 
The ectoderm at the fossa is strongly ciliated, the cilia being still obvious in 
preserved material, though this is not the case elsewhere on the column. 
The sphincter muscle (PI. xv., fig., 2) is an enormous, circumscribed, endodermal 
representative, hanging by a very narrow base from the floor of the fossa. ven 
to the naked eye it is a very pronounced outgrowth, 7 mm. in length. It 
breaks up into many large lobes, the appearance differing much in different 
sections, and in places seems to enclose portions of the ccelenteron. A narrow 
mesogleeal axis extends down the middle, and from it branching processes arise in 
a somewhat pinnate manner, and are continued into each lobe. A peduncle is 
practically absent, and the mesogleea of the sphincter is in continuity with that of 
the column-wall only within very narrow limits, the ordinary endodermal muscle 
being traceable nearly across the connexion. ‘The mesogloeal processes branch 
very much; the lining muscle fibres are not represented in the figure. Though 
differing in detail, and many times larger, it will be seen, on comparison of the two 
figures, that the muscle is exactly of the same type as that in S. helianthus 
(Pl. xiv., fig. 1). It is probably the largest circumscribed sphincter known in any 
Actinian. 
In radial sections through the disc, the tentacles are displayed as crowded, 
irregular, thin-walled, vesicular outgrowths of the disc; and, compared with those of 
the column, each of the three component layers undergoes some modification. 
The ectoderm loses its gland cells, and the outer half is constituted almost entirely 
of aclearly-defined zone of small nematocysts; the inner half of the ectoderm, on 
the other hand, appears as a nuclear zone. Neither an ectodermal nor an 
endodermal musculature is distinguishable, and the mesoglcea is nowhere plaited. 
The endoderm is very narrow, and brown pigment granules take the place of 
zooxanthelle. 
Where a section passes through a group of tentacles (Pl. x1v., fig. 3), the disc is 
indistinguishable from the tentacles themselves, and the two are practically alike 
in structure, the disc being thin-walled and possessed of a nematocyst layer; a 
