Stephenson — Certain Actiniaria collected of)' Ireland. 133 



body, the coelenteron is a good deal restricted. The primary mesenteries are 

 sterile; mesenteries of cycles 2, 3, 4 are fertile; those of 5 are. some of them, 

 those of 6 are rarely, fertile. Two actinopharyngeal grooves. Mesenteries of 

 all cycles bear filaments. I can see no marginal stomata in the perfect mesen- 

 teries, but small oral-stomata are present. In the young cycles, each pair for 

 the most part has one mesentery better developed than its partner. In the 

 majority of cases tins inequality follows the rule which prevails in Actino- 

 stota, but still there are a number of instances in which the inequality is 

 either too slight to be detected by dissection, or else is developed contrary to 

 rule. The mesenteries are normally developed, not on the type of the Endo- 

 coelactidae. They are flaccid, with weak musculature. Sections of a sector 

 taken at a fairly high level show the following details. The perfect mesen- 

 teries have a few short and simple or slightly branched processes on either side 

 where the mesentery leaves the body-wall, better developed on the side which 

 bears the retractor-muscle than on the other. These soon die out ; but about 

 the middle of the surface of the mesentery is a low, weak pennon, tapering 

 at both ends. Its best processes are fairly high and moderately branched ; 

 they are stout, but variable. Sometimes their appearance is fairly ordinary 

 (PL XVIII, fig. 1), while sometimes they contain so much mesogloea that 

 they give something like the "reversed" appearance which I have described 

 as characteristic of Leptoteiclms insignis (48). (PL XVII, fig. 16.) The medium- 

 sized mesenteries are similar, the musculature becoming weaker cycle by 

 cycle ; the longitudinal muscle processes hardly deserve the name " pennon," 

 and are confined to a small part of the mesentery immediately behind the 

 gonad or filament. (PL XVII, figs. 12, 13, 14, 15.) The smallest mesenteries 

 have parietal musculature only. Although the pedal disc is so small, distinct 

 basilar muscles are present. 



(ii) Sphincter. — Very small and weak for the size of the animal, and 

 weaker than in A. Sayinatus. It forms a narrow band in the mesogloea 

 (PL XV, fig. 1) a little below the uppermost rim of the body, and lies close 

 to the endoderm, although separated from it throughout by a narrow meso- 

 gloeal strand. It is of fairly uniform width throughout, tapering off below 

 and ending bluntly above. In transverse section the fibres are arranged in 

 small alveoli and clusters, and these aggregated into clumps of larger and 

 various size (PL XVII, figs. 10, 11); but it can hardly be described as a 

 clearly "alveolar" sphincter. The fibres are a good deal mixed up with dark 

 pigment-granules. 



(iii) Tentacles and oral disc. — Tentacular longitudinal muscles entirely 

 ectodermal. In the distal part of the tentacle it forms a very narrow fringe 

 of very short, quite stout, stumpy processes round the edge of the mesogloea 

 (PL XVII, fig. 18), many of them not much longer than wide, simple or a 



