TH. MORTENSEN. 



[REP. OF THE "iMICHAEL SARS" NORTH 



Ctenophores there are still many unsolved problems; it 

 is then not to be wondered at that this also holds good 

 for the deep-sea forms. 



The new form discovered by the "Michael Sars" 

 was taken on Station 64 (34° 44' N., 47° 52' W. 2000 m. 

 wire; 2i /6 1910), in young fish trawl, 2 specimens, one 

 large and one small; station 81 (48° 2' N. 39° 55' W., 

 1500 m. wire; 1T t 1910), in s /i m. net, fragments of a 

 large specimen. The small specimen was sacrificed for 

 sections, which, however, proved very poor and of little 

 use. The animai being very little transparent, it was 

 necessary, in order to study the anatomical structure, 

 to make dissections. For that purpose the fragments 

 from Stat. 81 proved very useful, so that the large spe- 

 cimen from Stat. 64 could be spared to some degree. 



The photographs (PI. I, figs. 1 — 4) were made by 

 Docent R. H. Stamm. I beg herewith to express my 

 thanks for his kind assistance. 



I shall describe this form under the name of 



Aulacoctena acuminata n. g., n. sp. 



The large specimen measures 45 mm. in length, 21 

 mm. in breadth. It is distinctly compressed after the 

 sagittal axis, measuring only 16 mm. in thickness. 



The outline of the body (PI. I, fig. 1) is ovate, 

 narrowing slightly towards the oral end. The aboral end 

 is produced into a long, slender process, measuring — as 

 is seen from the figure of the small specimen (PL I, fig. 

 3) — about Vs of the total length. (In the large specimen 

 this apical prolongation was partly lost, and this was also 

 the case in the broken specimen). Along each side of 

 the body, between the subtentacular costae, there is a 

 very deep furrow (PI. I, fig. 2), in the bottom of which 

 lies the tentacular apparatus. The furrow continues from 

 the oral end nearly to the tip of the apical prolongation. 

 The mouth edge forms two rounded lobes, in the trans- 

 versal plane; the corners are, however, not so deep as 

 would appear from fig. 2, the furrow being here some- 

 what split up at the lower end. Also between the other 

 costae the body may be somewhat depressed, but this 

 is evidently due to the preservation. 



The costae are nearly equal in length, the subten- 

 tacular ones being only slightly longer than the others; 

 they cease at about l U of the body length from the oral 

 end — judging from the furrows in which they are retractet; 

 the combs could not be discerned so far down. On the 

 aboral prolongation the costae continue nearly to the tip. 



The aboral prolongation is deeply invaginated on 

 the top, being thus a hollow tube. The bottom is slightly 

 widened and elevated in the middle, and here lies the 

 apical organ. (PI. I, fig. 5). The costae continue as 

 ciliated ridges down along the inside of the tube to the 



apical organ. (I have been unable to discern with 

 certainty more than 4 of them, but that all 8 costae 

 continue to the apical organ in the same way can scar- 

 cely be doubted). Of the structure of the apical organ 

 I can give no information. The polar fields continue 

 some way up the inside of the tube — how far, could not 

 be ascertained, the tip being broken; but in any case, 

 it will be nearly to the upper edge. Close to the apical 

 organ, in the bottom of the invagination, lie the two 

 excretory pores, in the typical oblique position, not 

 in the median sagittal line. 



The gastrovascular system. (PI. I, fig. 5 textfig. 

 1—3). From the rather small, flattened infundibulum 

 proceeds a short, spacious infundibular canal. The excre- 

 tory canals are very short; whether they are simple or 

 divided in the usual way, could not be settled; but the 

 fact that the pores lie distinctly to the side would seem 

 to indicate that they are divided, the one branch forming 

 a blind ampulla. The adradial vessels issue separately, 

 not from a common interradial vessel (see the diagram, 

 textfig. 3, compared with fig. 4, the diagram of a typical 

 tentaculate Ctenophore). The subsagittal adradial vessels 

 issue directly from the infundibulum, very close to the 

 median line. They proceed downwards, close to the 

 pharyngeal wall, for nearly half the length of the pharynx, 

 giving off sligthly branching, but not anastomosing, pro- 

 liferations along their inner and abradial, but not along 

 the adradial side. About halfway down a branch passes 

 outwards to the meridional vessel, while the adradial 

 vessel continues downwards, ending blindly (texfig. 1). 

 The subtransversal adradial vessels issue distally, over the 

 tentacle basis. They give off each one long branch, 

 which passes downwards as a simple canal, parallel to 

 the tentacle sheat, ending blindly. In the broken speci- 

 men only one of the adradial subtransversal vessels gave 

 off this branch (textfig. 1 and 2). 



The meridional vessels continue aborally from the 

 entrance of the adradial vessel nearly to the tip of the 

 apical prolongation. In their whole length the meridian 

 vessels give off numerous proliferations to both sides. 

 These are white and, as they lie close to the surface, 

 very conspicuous, forming one of the most prominent 

 features of the animal. They issue not regularly alterna- 

 ting or opposite and are alternatingly — but not regularly — 

 shorter or longer, the longer ones being often more 

 or less branched. They do not form anastomoses, but 

 may cover one another more or less, as they are so 

 numerous and large that there is not room for them all 

 in the same plane. Those issuing from the subtentacular 

 vessels along the lateral furrows are especially conspicuous 

 and beautifully arranged (PL I, fig. 8). None of the pro- 

 liferations pass through the jelly to the pharyngeal wall, 



