The material of Ctenophora collected by the "Michael 

 Sars" Expedition is not very large, but upon the whole 

 in a fairly good condition. The specimens are preserved 

 in formaline, which has the great advantage of keeping 

 them nearly as transparent as the living specimens. 



The species found are only five, viz. Pleurobrachia 

 pileas (O. Fr. Miiller), Mertensia ovum (Fabr.), Beroe 

 cucumis Fabr., Beroe Forskdli M. Edw. and a new 

 deep-sea Ctenophore, which is described here under the 

 name of Aulacoctena acuminata Mrtsn. That these five 

 species represent all the Ctenophores met with by the 

 expedition, is rather improbable. It can scarcely be doubted 

 that also some Lobate Ctenophores have been taken, but 

 as these can only be preserved when treated separately 

 and with the utmost care, it could not be expected that 

 specimens should be found in the preserved materail, it 

 being nearly impossible on such an expedition to find 

 the time necessarry for the proper treatment of these 

 difficult objects. 



While the four firstnamed species afford little interest 

 beyond the distribution, the deep-sea form is of unusual 

 interest. Hitherto only two deep-sea Ctenophores have 

 been found. The German Deep-sea Expedition, by which 

 deep-sea Ctenophores were for the first time observed, 

 found in the Atlantic and Indian Ocean a form apparently 

 allied to Mertensia. The same form was also taken by 

 the German South Polar Expedition, one specimen off 

 Kerguelen, another off the Cap Verde Islands, and was 

 described by Dr. F. Moser 1 ) under the name of Mertensia 

 Chuni. Also a deep-sea Cydippid was taken by the 

 German deep-sea Expedition ; it is still known only from 

 the short notice given by Chun 2 ). The new form dis- 

 covered by the "Michael Sars" is thus only the third 

 deep-sea Ctenophore made known, and from that reason 

 alone may attract attention. The study of its ana- 

 tomy has considerably increased its importance. While in 

 general it agrees with the morphology of the Ctenophores 



>) F. Moser: Die Ctenophoren der deutschen Siidpolar-Expe- 

 dition. Deutsche Siidpolar Exp. 1901—1903. Bd. XI. Zoologie III 

 1909, p. 126, Taf. XX Fig. 1—4. 



2 ) C. Chun: Aus den Tiefen des Weltmeeres. II Aufl. 1905. 

 p. 545, 



as hitherto known, especially from the surface forms, it 

 affords several new and important features, which neces- 

 sitate the establishment not only of a new genus for it, 

 but also of a new family, to which the „Mertensia" 

 Chuni evidently likewise belongs. 



It would be very interesting to learn the anatomical 

 structure of the deep-sea Cydippid from the German 

 Deep-sea Expedition, in order to see, whether this form 

 perhaps also belongs to the same family. That it is stated to 

 be a "Cydippe", evidently, means nothing more definitely 

 beyond the fact that it is a tentaculate Ctenophore of the 

 order Cydippidea. This concerns the question, whether 

 all deep-sea Ctenophores belong to the same family or 

 whether deep-sea forms have developed within several 

 of the larger groups of the Ctenophores. It is, of course, 

 impossible to say anything more definitely at present 

 about this very interesting problem, so long as the whole 

 number of deep-sea forms known amounts to no more 

 than three, of which only two have been studied. But 

 the fact that these two forms, though so very different 

 looking, appear to be nearly related, is already suggestive, 

 and it is certainly not inappropriate to call attention to 

 the problem already now. 



That there will prove to exist still more deep-sea 

 Ctenophores, can scarcely be doubted. It is noticeable, 

 it is true, that only these few forms have been found in all 

 the many deep-sea tow-nettings hitherto carried out, and 

 this is certainly not suggestive of the existence of a great 

 number of different forms of deep-sea Ctenophores. But the 

 fact that only so few specimens of these forms have been 

 found counterbalances this evidence. It is beyond doubt 

 that these forms must exist in vast numbers somewhere 

 - this is simply necessary for the existence of the species. 

 But when we have in all found only 6 specimens of 

 one form ("Mertensia" Chuni), 3 of another (the new 

 form from the "Michael Sars") and one specimen of the 

 third (the Cydippid of the German Deep-sea Expedition), 

 this fact evidently means that there still remains much 

 to be discovered in regard to the occurrence of these 

 forms — and there are then ample possibilities for the 

 existence of other, hitherto undiscovered forms among 

 them. Even with regard to the occurence of the surface 



