ACTINIARIA 



these in the filaments. If spirocysts really are present, they are at any rate \-ery rare. The ectoderm of the 

 pedal disc is provided with very weak, radial nuiscles. The mesogloea is thin and only at the inser- 

 tions of the mesenteries very nmch thickened. It is homogeneous, witli sparsely scattered and ramificated 

 cells, the mesogloea has, however, this appearance in all parts of the body. 



The ectoderm of the column is of equal height and contains, in addition to the supporting cells, 

 numerous mucus-cells, while I have not observed any granulous gland-cells. It ought to be mentioned that 

 no such cells have been discovered by me in the ectoderm of the tentacles or in the oral disc, only in the 

 filaments and very sparsely in the ectoderm of the actinopharynx they seem to be present. Typical spiro- 

 cysts are found in the ectoderm of the colunm, in the small elevations of the distal part they are most nu- 

 merous, in the proximal part more sparse. The papiUiform elevations are almost exclusively thickenings of the 

 ectoderm, only in a small degree the mesogloea takes part in the composition of the papillae which contain 

 very numerous, densely packed spirocysts; the jiarts of the ectoderm between the papillae are on the other 

 side more destitute of spirocysts. At the base of the ectoderm there is a weak stratum of nerve-fibrillae and 

 nerve-cells and also a distinct, though weak layer of longitudinal nmscles (textfig. i) which are especially 

 conspicuous in preparations stained with iron-haematoxylin. The mesogloea is rather thick ))etween the 

 furrows, while Danielssen says that it is thin. This difference must, however, certainly be referred to the 

 unequal state of contraction of the type specimen and of the specimen from Sunde, examined more in detail 

 by myself. The inner part of the mesogloea is homogeneous here as also in the mesenteries; in the outer parts 

 cells and now and then fibrillae are scattered or accumulated. Danielssen has interpreted the fibrillae 

 as mesogloeal, circular muscles. In reahty the circular muscles of the column are very weak and endodermal 

 and form no spliincter. The endoderm is high and provided witli numerous nuicus-cells. 



The ectoderm is higher in the smooth, hemispherical ends of the tentacles than in the the other part 

 of the tentacles which is set with elevations, and much thicker than tlie mesogloea, and in all places of 

 the same height (textfig. 2). It is characteristic by its abundance of stinging capsules, l)y wliicli the apex 

 of the tentacles form strong batteries. In addition to connnon s]nrocysts of the same appearance as those 

 of tlie column there are large stinging capsules with densely rolled-up thread and of considerable size (86 — 

 108 X 12 — 14 n — sometimes there are still larger capsules). Besides, I ha\e here observed very large, irre- 

 gularly formed capsules, of a granulate appearance and of variable length which are probably stages of 

 development of the former. I have namely found capsules of an intermediate shape, that is to saj"^ capsules 

 which in form and granulation agree with the latter, but in the appearance of tlie spiral tliread with the 

 former. All these capsules are. however, rather rare, wliereas another sort of capsules is very common. They 

 are drawn out, of equal width, with distinct basal part to the spiral thread and much thinner than the large 

 spirocysts (55 — yy x 5 //). Their thread is very twisted and its windings, close by the basal part, very di- 

 stinct. Stages of development of these capsules with indiscernible thread are also found. At last there ap- 

 pear smaller capsules of the same appearance as the drawn-out capsules but of smaller sizes (24 — 29 X about 

 3 fi). The stratum of ner\-e-fibrillae is distinct, but not thick, the muscles of the ecto- and endoderm 

 weak. The mesogloea is mostly very thin, the endoderm thick. The proximal part of the tentacles, carrying 

 elevations, is built just as the distal part of the column. The spirocysts are verA- numerous in the elevations 



The Ingolf-Expediunn. V. 9. 2 



