Part II. — Stichodactylince and Zoanthece. 149 



The base is very spreading, irregular in outline, and firmly fixed to coral 

 rock, adapting itself to the irregularities of the surface ; in diameter it is larger than 

 the column. A brownish, cuticular layer occurs between the ectoderm of the base 

 and the surface of attachment, and may either be detached with the polyp or 

 remain adhering to the rock. The internal, radiating mesenterial lines are clearly 

 indicated through the thin basal-wall. 



The column is short, thin-walled, and semi-transparent, the mesenterial lines 

 showing through ; the surface is smooth, and thrown into delicate longitudinal 

 ridges and furrows, and occasionally transverse wrinklings are indicated. The 

 limbus is spreading and irregular, and the polyps are generally constricted a little 

 above the middle. The upper region of the column and the disc usually overhang 

 so as to hide the parts below. Individual polyps are generally oval in outline in 

 transverse sections. 



A single cycle of very short tentacles occurs at the apex of the column or 

 margin of the disc, a longer tentacle alternating with a short one, or there may be 

 two or three of the latter between two longer ones. Much irregularity occurs in 

 this respect. In shape the tentacles may be shortly acuminate, or cylindrical and 

 rounded at the tips. A small, nearly horizontal, tentaculiform outgrowth projects 

 from near the base of many of the larger tentacles, and, occasionally, from the 

 middle tentacle of an alternating three. 



The disc is divisible into two regions : a peripheral, naked area, limited out- 

 wardly by the marginal cycle of tentacles ; and a larger, inner area bearing the 

 branching outgrowths described as tentacles. The peripheral j)ortion of the disc is 

 very thin, and sometimes stands as a distinct parapet or collar around the inner part; 

 at other times it is entirely reflexed (PL x., fig. 3). The discal tentacles are very 

 short, thick, columnar outgrowths which divide towards the apex into numerous — 

 6 to 12 — small, tubercular, finger-shaped, or pointed processes. A few, irregularly 

 arranged examples may occur near the mouth, or they may be practically absent 

 from this region. The organs are capable of assuming the flaccid condition, or 

 one of distension, independently of one another. They may be distributed over the 

 whole disc except near the margin, but are always less numerous centrally. The 

 distinction between the discal and the perioral series is not always apparent. 

 Usually the tentacles appear irregularly disposed, but occasionally an arrange- 

 ment in cycles, or, more often, in radial series, is evident. It is doubtful if 

 more than two or three ever communicate with the same mesenterial chamber 

 (PI. x., figs. 3-6). 



In the living condition the disc usually overhangs so as to hide the base and 

 column ; but the peripheral, naked portion of the disc may be vertically elevated 

 as much as 4 mm. above the central part. In retraction the capitular part of the 

 column closes over the rest of the disc as a thin, radiately marked, Semi- tranS- 

 TKANS. ROY. DUB. SOC, N.S. VOL. VII., PAET VT. Z 



