Stkphknson — Certain Actiniaria collected off Ireland. 12o 



distinction of a pennon. The larger mesenteries (1st and 2nd cycles) have a 

 similar fringe in their proximal part, but in the distal part it rises gradually, 

 till it forms a feeble pennon, with moderately high processes, which are never 

 much branched, and often simple. It ends abruptly, and leaves a narrow 

 non-muscular part behind the filament. (PL XVII, fig. 14.) 



Here and there a little muscle is embedded in the mesogloea. The parieto- 

 basilar muscle, at the level of my sections, is weak, and extends over the 

 greater part of the opposite surface of the mesentery to the pennon. Its 

 distal ending varies, even in two mesenteries of the same pair — it may taper 

 away, or form a slight hump, or even a small free fold provided with a few 

 little stumpy processes. 



(ii) Sphincter. — Fairly large. It must be very strong to be able to contract 

 enough to close up such a stiff animal. It is long (PI. XIV, fig. 10, shows its 

 position), and lies throughout against the endoderm. It is at its best develop- 

 ment about the middle, being very irregular above on account of the folds into 

 which the wall is thrown, and their continuity with the tentacle-bases. Below 

 it rapidly narrows into a long tail. This lower part is cleanly marked off from 

 the rest of the mesogloea, and is reticular (PL XVII, fig. 9) in structure, the 

 meshes being often large, with a tendency to transverse elongation, and fine. 

 From about the middle upwards the reticular structure becomes gradually 

 alveolar, more and more mesogloea intervening between the muscle-cavities. 

 The upper part is poorly and irregularly developed, the scattered cavities 

 varying very much in form. In addition to a tendency to transverse elonga- 

 tion of the cavities, there is a distinct but vaguely marked vertical layering. 

 One can hardly tell where the body-wall ends and the tentacle-bases begin. 



(iii) Disc and Tentacles.— The radial musculature of the disc is much better 

 developed in the sections I have than the longitudinal musculature of the 

 tentacles. It forms a well-defined band of varying width, embedded in the 

 mesogloea, and at its best not occupying more than about 4/ of the width of 

 the mesogloea. It lies sometimes about the middle, sometimes near the ecto- 

 dermal side of the mesogloea. Where best developed the muscle cavities are 

 close enough together to give the band a reticular structm-e, but in the thinner 

 places the cavities are more scattered, and the band is only one or two cavities 

 deep. It is usually interrupted or thinned out above the insertions of larger 

 mesenteries. The mesogloea of the tentacles is extremely thick, especially at 

 the base, where it is almost equally thick all round iu some places. The 

 mesogloeal longitudinal muscle (PL XVII, fig. 5) is very feeble, especially 

 near the base, where it lies near the ectodermal surface, often as a single row 

 of cavities. Even in the thin part of the tentacle it seems better developed 

 on the inner than the outer side. 



