CTENOPHORA. g. 



appears uot to occur in the Greenland vSeas, as also Romer (Op. cit. p. 76) and Damas & Koefoed 

 (Op. cit. p. 413) state that it does not occur under high-arctic conditions. The more remarkable is the 

 fact that it occurs in the antarctic regions under conditions corresponding to the most arctic (Moser. 

 Ctenoph. d. deutsch. Siidpolar-Exp.) — so remarkable, indeed, that one can scarcely help thinking that 

 it may, perhaps, not be really this species. 



While these three species are thus of little or no value for judging of the currents, the case 

 is quite different with Mcrtensia ovimi. This is a true arctic form, not occurring outside the polar water, 

 and if it is found in some place, where it does not occur usually, it affords the proof that arctic water 

 has intruded — and I would even be inclined to reverse the statement, viz. that where Mcrtensia ovum 

 does not occur, there is no polar water. 



This has an important bearing upon the question, whether the polar water reaches the North 

 European Seas, as is maintained by Aurivilliu s') and Chun-). "Ini Laufe des Winters kann das 

 Plankton der kalten Stromgebiete sich so weit nach Siiden vorschieben, dass von den vereisten Fjorden 

 West-Gronlands in dem Smith-Sund und in der Baffinsbai bis nach Helgoland und in die westliche 

 Ostsee eine einheitliche arktische Fauna die Oberflache bevolkert". (Chun. Op. cit. p. 8). The proof of 

 this Chun finds in the occurrence in these waters of such forms as Plciirobracliia pilcus, Bolina in- 

 fimdibulum and Beroe cucumis, the Siphonophore Dipltycs arctica, and the Appendicularians Oikopleura 

 labradoriensis and FriHUaria bor calls, while Aurivillius mentions as "arktisch im engen Sinne": 

 Sagltta arctica, the Crustaceans Calamis Iiypcrborcus, Euchcrta iiorvcglca, Metrldla longa, Euphausia 

 Incriiils and the Pteropod Cllone liuiaclna (Op. cit. p. 87—91). That the Ctenophores named are really 

 without value as a proof of the presence of arctic water, is already sufficiently explained, and the 

 same appears to hold good of all the other forms. Of Dlphycs arctica Damas & Koefoed (Op. cit. 

 p. 414) state that "sa distribution est independante de la temperature, de la salinite et de I'origine des 

 eaux dans lesquelles il se trouve"; Frlflllarla bor calls is known also from the Mediterranean and the 

 Bismarck Archipelago. Without entering on a more detailed discussion of the geographical distribution 

 of all the forms mentioned above — (most of them are given in "Nordisches Plankton" as distributed 

 over the North Atlantic down to ca. 50°— 60° N.) — I must express my conviction, in perfect accord- 

 ance with Damas & Koefoed (Op. cit.), that not one of them is really and exclusively arctic and 

 thus cannot be taken as a proof of the intrusion of arctic water into the North-Sea and Skagerak. — 

 Mcrtensia ovum, if definitely proved to occur there, would give the indubitable proof of the intrusion 

 of arctic waters here ; but there is no proof that this species really occurs in these Seas (Comp. above, 

 p. 65). I quite agree with Moser (Ctenoph. d. deutsch. Siidpolar-Exp. p. 180) that the fact of Mcrtensia 

 ovum not occurring here is a proof that the arctic waters do not reach so far South in the North 

 European Seas, "denn andernfalls ware nicht einzusehen, warum Mcrtensia ovum nicht zeitweise auch 

 hier, wie an der amerikanischen Kiiste, weiter siidlich vordringeu sollte". — This result is in accord- 

 ance with the view of the hydrography of these seas set forth by Martin Knudsen'') where the 

 polar stream is stated not to reach the North European Coasts. 



M Carl W. S. Aurivillius. Vergleichende thiergeographische Uiitersuchuiigen fiber die Plankton-Fauna der vSkage- 

 raks in den Jahren 1893— 1897. Kgl. Sveuska Vetensk. Akad. Handl. Bd. 30. 1898. (p. 133— 135)- 



^) C. Chun. Die Beziehuugen zwischeu dem arktischen und antarktischen Plankton. 1S97. 



3) Martin Knudsen. Havets Naturlaere. Hydrographi, med sjerligt Hensyn til de danske Farvande. Skrifter udg. 

 af Konmiissionen for Havundersogelser. Nr. 2. Kobenhavn 1905. 



