CERIANTHARIA. 



may occasionally be absent. This is often the case with the directive (median) labial tentacle, which 

 is absent in Cerianthus lloydii, valdiviae, Pachycerianthus multiplicatus, maua, Arachnanthus oligopodus, 

 sarsil, Arachnactis lobiancoi. Botrucnidifer norvegicus, whilst it is found in Cerianthus membranaceus 

 and vogh\ Pachycerianthus solitarins and Ceriantheopsis amcricanus. In Botrucnidifer norvegicus, Ceri- 

 autlius vogti and probably also in Pachyccrianthus multiplicatus and Arachnanthus sarsi, the chamber 

 contiguous to the directive chamber on either side of the animal is without a labial tentacle. Irre- 

 gularities in the tentacle arrangement occur not infrequently, and this is specially true of P. solitarius. 

 Probably we have here disturbances of growth, as they are accompanied by irregularities also in 

 the arrangement of the mesenteries. Where to look for the cause of these disturbances, I cannot at 

 present tell. Sometimes the tentacles are lacking in adult animals, as in C. lloydii and A. sarsi, or 

 else are very small. In that case the animals are in a state of regeneration, the upper end of the 

 animal having been torn off. Danielssen has not taken account of this in describing C.borealis 

 (= C. lloydii}, nor has Me. Murrich (1893) in his description of Cerianthus vas. 



The tentacle arrangement in Ceriantharia is related for the most part to the size of the animal. 

 In no case however have more than 4 cycles been observed. 



2. Stomatodaeum, siphonoglyph, hyposulcus and hemisulci. 



The stomatodaeum shews a like structure in almost all the adult Ceriantharia which I have 

 examined. The ectoderm forms high longitudinal ridges, which in the oral portion of the stomato- 

 daeum are not supported by mesogloeal ridges, but in the aboral portion are found covering such 

 ridges. In the oral portion of the stomatodaeum, there is no great difference in structure between 

 the ectoderm on the longitudinal ridges and that in the furrows; in the aboral portion where meso- 

 gloeal ridges are found and where in consequence the ridges are considerably higher and the furrows 

 deeper, the structure of the ectoderm in the ridges and in the furrows is different. The ectoderm 

 lining the furrows consists chiefly of supporting cells, which at the point where the passage into the 

 filaments occurs acquire very long cilia. On the other hand in the ectoderm of the ridges, in addition 

 to supporting cells, are found numerous mucus cells and both spirocysts and thick-walled nematocysts, 

 the last of the same appearance as in the cnido-glandular tract (for details see p. 15). 



An exception to this rule is shewn by the two representatives of the genus Arachnanthus, 

 A. oligopodus and sarsi. In this genus no mesogloeal ridges are found in the stomatodaeum, in other 

 words the longitudinal ridges of the stomatodaeum are formed exclusively of ectoderm, and the 

 difference too in the histological structure of the furrows and ridges is insignificant. 



The siphonoglyph in the Ceriantharia is more or less developed. It is characteristic of the 

 Ceriantharia that almost always a number of mesenteries besides the directives are attached to the 

 siphonoglyph. In Botrucnidifer norvegicus only the directive mesenteries are attached to the sipho- 

 noglyph. In all representatives of the genus Cerianthus and in Ceriantheopsis the siphonoglyph is 

 not very broad though at least 4 mesenteries are attached to it. In the genus Pachycerianlhus it is 

 broader as a rule, and sometimes, in P. aestuarii, (according to Torrey and Kleeberger's account) 

 may become quite broad, seeing that no less than 16 mesenteries are there found united with the 

 siphonoglyph. In relation to the size of the body and the total number of mesenteries the siphono- 



The Danish Ingotf-Expeililion V. 3. 7 



