CERIANTHARiA. .^ 



49 



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

 is absent in Crrianthus lloydii, valdiviar, Pachyccriantliiis iintltiplicahis, maua, Araclniantlms oligopodns, 

 sarsil, Arachnactis lobiancoi. Botrucnidifcr norvrgicus, whilst it is found in Ccriantlius mcvibranacrus 

 and vogti^ Pachycfn'aii//n/s solifariiis and Ccnaiifhropsis amcricanus. In Botrucnidi/cr norvficus Crri- 

 anthus vogfi and probably also in rachycrricnitliux inulliplicahis and Arachnanf/ius sarsi\ the chamber 

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

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

 Probably we have here disturbances of growth, as the)- arc 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. Dauielssen has not taken account of this in describing C.bor talis 

 (= C. lloydii), nor has Mc. Murrich (1893) i" ^"s description of Ccriantlius vas. 



The tentacle arrangement in Ceriantharia is related for the most j)art 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 ectodenn 

 lining the furrows consists chiefly of supporting cells, which at the point where the j^assage 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 Arachnanthns, 

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

 words the loneitudinal ridees of the stomatodaeum are formed exclusivelv 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 Botrncnidifcr norvcgicus only the directive mesenteries are attached to the sipho- 

 noglyph. In all representatives of the genus Ccriantlius and in Ccrianthcopsis the siplionoglyph is 

 not ver>- broad though at least 4 mesenteries are attached to it. In the genus Pachyccriavtluis it is 

 broader as a rule, and .sometimes, in P. acstnarii, (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 Ingolf-Expedition V. ;. ^ 



