ACTINIARIA 



mination is in several points incomplete. The ectoderm of the column is high and contains numerous mucus- 

 and sparse albumen-cells. In the central part of the elevations the mucus-cells are still sparser, while the 

 main part of the cells is formed by supporting cells and numerous nematocysts which latter are rather sparse 

 in the other part of the column. The nematocysts are 26 29 X 2,5 ft in size. The elevations thus may be 

 regarded as weak batteries of nematocysts as in Halodava, though they are not ampullaceous as in this genus, 

 but compact and supported by an off-shoot of the mesogloea (textfig. 140). The cinclides and the apertures 

 of the physa are of the same structure. The ectoderm as well as the endoderm are invaginated, and the aper- 

 tures are surrounded by rather strong circular muscles belonging to the endoderm (textfig. 141). The meso- 

 gloea of the column is thicker or thinner than the ectoderm, according to the different state of contraction. 

 It is fibrillary and contains rather numerous cells with a scanty amount of protoplasm. The endodermal 

 circular muscles are very strong and form palisade-shaped folds, not concentrated so as to form a sphincter. 

 Strong parts of these muscles, as usual, break through the mesenteries. The uppermost part of the tentacles, 

 the acrospheres, are, as in Halodava, of another structure than the other part of the tentacles, the peduncle. 

 The ectoderm is very high and provided with very numerous nematocysts with slightly visible basal part 

 to the spiral thread. They reach a size of 120 202 X about 4 ft, and are rib-like. The tentacles, as well as 

 all other parts of the animal, are devoid of spirocysts. The nerve-layer is distinct, the ectodermal muscles 

 very weak. The mesogloea contains rather numerous cells, poor in protoplasm, and it is about half or one 

 third as thick as the ectoderm. In the mesogloea I have observed fibres, now straight, now folded, now run- 

 ning along the tentacles, now in transverse direction and terminating partly in the endoderm, partly in the 

 ectoderm, apart from the nerve-layer. I cannot with certainty decide the nature of these fibres, but it is 

 not very probable that they are nerve-fibrils, as they are much thicker than such fibrils; I am more inclined 

 to think that they are nematocyst-threads having been thrown into the tissues of the animal by the ejec- 

 tion of the nematocysts, on account of an abnormal position of certain nematocysts. The endoderm is of 

 about the same thickness as that of the mesogloea. The main part of the tentacles, the peduncle, is provided 

 with a rather high ectoderm, containing numerous mucus-cells and sparse albumen-cells. The nematocysts 

 display an indistinct basal part to the spiral thread and reach a size of 20 24 X 2,5 p. The nerve-layer is 

 well developed, so are also the longitudinal muscles, the folds of which in transverse-sections are dichoto- 

 mously branched and of about the thickness of the ectoderm. The mesogloea is of the same structure as in 

 the apex and attenuated towards the base. The ectoderm of the oral disc is of ordinary height and contains 

 sparse nematocysts with indistinct basal part to the spiral thread, 17 19 X 2 p in size. Their ectodermal 

 muscles recall those of the peduncle of the tentacles. The mesogloea and the endoderm are thin. The ecto- 

 derm of the actinopharynx is very high and provided with numerous, rib-like nematocysts, 53 65 X 5 ;t 

 in size, and long, close albumen-cells. Their mucus-cells are sparse. The ectoderm is much higher in the ridges 

 than in the furrows. The ectoderm of the siphonoglyphe is also very high, provided with smaller albumen- 

 cells, but devoid of nematocysts. There is no such strongly ciliated boundary streak to be found here as in 

 Peachia (compare p. 102). The nerve-layer is rather distinct in the actinopharynx. There are also very weak 

 ectodermal longitudinal muscles. The mesogloea and the endoderm are thin in the actinopharynx, in the 

 siphonoglyphe however thick. 



The Ingolf Expedition. V. 9. *5 



