Stephenson — Certain Actiniaria collected off Ireland. 141 



off towards the body-wall. Here, the processes may be sufficiently stout to 

 give the "reversed" appearance. The musculature of the exocoelic face of 

 the mesentery is weak; no free fold is formed at the level sectionized at any 

 rate"), though there is sometimes a fringe of stumpy processes. (For mesentei ie£ 

 see PI. XVIII, figs. 13, 14.) 



(ii) Sphincter. — This is separated throughout from the endoderm by a 

 narrow strip of mesogloea which widens out at the top. It almost entirely 

 tills the narrower parts of the rest of the mesogloea just below the body-margin. 

 The upper extremity is rounded and well defined, and below it tapers off 

 suddenly to a point. Its structure may be termed alveolar, the alveoli being 

 mainly somewhat elongated transversely, often irregular, indefinite, and partly 

 collapsed (probably due to imperfect sections). They are most crowded in 

 the uppermost part, and they thin out and become small towards the side 

 of the muscle nearest to the ectoderm. There is a certain tendency to 

 arrangement in horizontal lines. 



(iii) Oral disc and tentacles. — The radial musculature of the oral disc is 

 partially embedded in the mesogloea iu the places where it is well developed, 

 and it is also similar to that of 0. coccinca in its peculiar plan of arrangement. 

 That plan is described iu detail under C. coccinca. The longitudinal musculature 

 of the tentacles is entirely ectodermal, and is well developed. (PI. XVIII, 

 fig. 16.) It is stronger than in C. coccinca,, and is supported on short processes 

 of the mesogloea, on which the fibres are arranged in a tufted way, giving a 

 characteristic appearance. The basal swellings of the tentacles have, of 

 course, a prominent development of mesogloea, but the ectoderm and its 

 musculature are poor there, the latter thinning away to very little. Elsewhere 

 the ectoderm is high, the musculature on the average not occupying more 

 than \ .of its thickness. 



tiv) General histology. — The tentacle ectoderm has a very clear and distinct 

 nerve-layer; the nuclei of the supporting cells are rather large, and very dis- 

 tinct, scattered generally. The spirocysts vary enormously in size, and are 

 often broad; they are not very long, but are very numerous in the outer part 

 of the ectoderm. A few fairly long thick- walled sting- cells, much narrower 

 than the spirocysts, and a fair number of rather small gland-cells are present. 

 The ectoderm of the body-wall, when preserved, varies; at its best it is 

 pretty well developed, with the nuclei mainly concentrated in t he inner pail, 

 and with numerous gland-cells, of which many are elongate, and reach from 

 the inner surface of the ectoderm to the outer. Also, a few fairly large and 

 broad l hick-walled cnidae are present. The epithelium is overlaid in places 

 with patches of dirt and mucus. The endoderm does not present special 

 features— there are well-developed, often folded ciliated lobes to the fila- 



