122 Proceedings of the Royal Irish Academy. 



sections got mixed; but I am inclined to think that the larger meshes 

 represent the outer, the smaller the inner, part of the disc. 



In the tentacles the longitudinal musculature is also entirely mesogloeal, 

 and runs in a narrow, almost straight band through the mesogloea, fairly 

 near the endoderm. (PL XVII, tigs. 1, 2.) It is better developed in some 

 places than in others, and sometimes more wavy than others. In structure 

 it is alveolar, sometimes tending to be reticular, and is often only a single 

 chain of alveoli. These latter vary a good deal in size, some being fairly 

 large. At the bases of the tentacles, where the sections pass through the 

 basal swelling (PI. XVII, fig. 1), it is seeD thai .is the band of muscle reaches 

 the swelling it thins out rapidly, so that at the hack of the swelling it is 

 reduced to practically nothing. The mesogloea of the tentacle is thicker 

 than either of the other layers, and its niter side is much folded, in con- 

 sequence "i the surface-wrinkles,. and of course the ectoderm follows its out- 

 line. The basal swelling has a coating of ectoderm ; but it gets thinner and 

 thinner as the hack of the Bwelling is reached, and there it is very low and 

 poor. 



(iv) General histology. — The specimen seotionized is a male. Well- 

 developed ciliated 1" ent in the mesenterial filaments, and have 



their nuclei mainly concentrated in the inner parts; the glandular lobes 

 rout tin man. granular gland-cells. The whole endoderm in this 



species is rather particularly interesting, and contains elements of unusual 

 appearance whose detailed Btudy must be lefl foi the present. Among other 

 things, there are objects which apj rge and curious parasitic algal 



cells with a shining test and possibly a spiral thickening in the wall. 



derm is well developed, with scattered pigmenl and very 

 numerous spirocysts, which, though no) very br< ag —often nearly as 



long as the depth of I srm. Nerve-layer distinct. Gland-cells present 



in the inner part ; also a few of the presumed parasitic algae. The ectodermal 

 margin of the mesogloea appears to have a feeble fringe of muscle fibres, quite 



tinct and apart from the real longitudinal musculature; but I cannot be 



tain about this point. The ectoderm contains narrow, thick-walled cnidae, 

 longer than those found in the body-wall. The ectoderm of the body-wall is 

 low. not pigmented, with small scattered nuclei. A good many quite shor! 

 rat! iw, thick-walled cnidae (PI. XVI, fig. lljare present, and one sees 



even, very rarely, a spirocyst — though these may have stuck to the ectoderm 

 surface accidentally, coming from some other part. There are numerous large, 

 transparent, apparently glandular cells with fine granule- which absorb eo 



(v) The only other species of the genus Actinostola beside this one, which 

 have basal swellings to the tentacles, are -4. Carlgreni, Wass., and A. imiermet 



