Part II. — StichodactylincB and ZoanthecB. 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 zooxanthellse, and such is the case throughout the 

 polyp. For some distance from the mesogloea 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 verrucae 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 verrucse 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. Even 

 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 coelenteron. A narrow 

 mesogloeal axis extends down the middle, and from it branching processes arise in 

 a somewhat jjinnate manner, and are continued into each lobe. A peduncle is 

 practically absent, and the mesogloea of the sphincter is in continuity with that of 

 the column-wall only within very narrow limits, the ordinary endodermal muscle 

 being traceable ueai-ly across the connexion. The mesogloeal processes bi'anch 

 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 

 (PI. 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 vnth 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 a clearly-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 mesogloea is nowhere plaited. 

 The endoderm is very narrow, and brown pigment granules take the place of 

 zooxanthellse. 



Where a section passes through a group of tentacles (PI. xiv., 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 



