ZOANTHARIA 



17 



very instructive figure of a transverse section in PI. 59, fig. 6. It must be observed however, that iu 

 my specimens the strands of the mesogloea, separating the different parts of the ectoderm from each 

 other, do not always lie so closely as in this figure. 



As mentioned by H addon and Shackleton the sphincter is not strongly developed, espec- 

 ially if the size of the polyps is taken into consideration. In the distal part of the sphincter, however, 

 the fibres occupy almost the whole breadth of the mesogloea, the lower third part of the sphincter 

 being inconsiderable. H add on and Shackleton state that "no cavities are visible, the fibres 

 being completely embedded in the substance of the mesogloea." This is not the case in my specimens. 

 In the proximal part, where the muscle-meshes (in transverse sections through the sphincter) are small, 

 it may be possible that there sometimes are no cavities, in the distal part on the otlier hand the 

 muscle-meshes are large and as usual extend in a transverse direction. The parts of the mesogloea 

 lying between the muscle-groups are very small. The sphincter is thus fairly strong in this regard. 

 The ectoderm of the tentacles is high, the mesogloea on the other hand is thin as also the 

 layer of longitudinal muscles. In the ectoderm very numerous spirocysts are found. Whether thick- 

 walled nematocysts occur is uncertain, but if present they are very scarce. 



The ectoderm of the oesophagus is fairly high and provided with numerous, thick-walled 

 nematocysts (length 23-29/^, generally about 24— 26 /i). The mcsoglcca is fairly thin. In tlie 

 siphouoghphe the ectoderm is considerably thicker than in tlie oesophagus, witli the condition reversed 

 as regards the mesogloea. The mesogloea iu the siphonoglyphe is almost homogeneou.s, as cells and 

 cell-islets onh- occur very seldom. 



The number of mesenteries is greater than in any other northern Zoantliaria. In a small 

 polyp I counted namely 64 mesenteries, 17 macro and 15 micro on each side, in a large one 80 

 mesenteries. The macro-mesenteries are in the oesophageal region fairly thick, owing to the fact, 

 that the mesogloea is well-developed here, whereas it becomes thinner below the oesophagus. The 

 longitudinal muscles are not strong and the muscular plaits few. The parieto-basilar muscles are very 

 weak and narrow. None of these muscles are expanded in the bod>-wall. The micro-mesenteries 

 are very weak - the weakest I have ever seen — and do not reach above the entoderm of the 



body-wall. 



The filaments have the usual structure. They contain nematocysts with greatly twisted thread, 

 but not in great number. They are oval and fairly small (length 19-25^, breadth 10-12 //). Further, 

 they contain fairly many thick-walled, rather transparent nematocysts with distinct spiral thread and 

 broader at the one end, with varying length (19-24-26-31 /., breadth 6-7 /i) and also some thick- 

 walled, narrow, typical nematocysts (length about 26 /i). 



The species is dioeciou.s. 



The carcino'cmm. The ccenenchyme and the caual-s)stem have not been examined by H addon 

 and Shackleton. The outer layer of the ectoderm had fallen off. The mesogloea sends out a 

 number of fine outshoots, the presence of which indicates that the ectoderm is also discontinuous 

 here. On the inner side the ectoderm is thin and discontinuous with a well-developed cuticle. On 

 the outer side of the carciuteci.nn the mesogloea is very thick, on the inner side it is thin. The 

 entodermal canal-system (c, text-fig. 3, P- 13I thus lies quite close to the inner side of the ccenenchyme. 



The Ingolf-Expedition. V. 4. 



