MEDUSA. I. 



Some of the material in the Zoological Museum of Copenhagen has previously been worked 

 up and mentioned in the literature. Some older material has been examined bj- E. Haeckel and 

 mentioned in his Svstem der Medusen. The museum possesses a list of that material, to which Haeckel 

 himself has added the identifications of the species. The numbers in the list are refound in the labels 

 of the .specimens. The said Hst is of considerable interest, as far as it has rendered it possible to cor- 

 rect some of Haeckel's identifications. The medusae from Greenland were dealt with by G. M. R. 

 I^eviusen in "Meduser, Ctenophorer og Hydroider fra Gronlands Vestkyst" 1892, and, later, by the 

 present author in "Medusae collected by the "Tjalfe" Expedition" (1913), and "Meduser og Siphonopho- 

 rer" in Conspectus Faunae Groenlandicoe (1914). The la.st-mentioned paper includes a complete account 

 of the literature relating to the medusae of the waters of Greenland. 



Besides the older material, the collections of the following expeditions have been employed in 

 the present paper: 



Wm. Lundbeck, 1892 (Iceland). 



Danish "Ingolf" Expedition, 1895 and 1896 (Faeroe Islands, Iceland, and Greenland). 



Inspecting-ship "Diana", A. Ditlevsen, 1902 (Iceland). 



"Michael Sars", Ad. vS. Jensen, 1902 (Norway and Iceland). 



"Michael Sar.s", 1903 (Norwegian Sea). 



Inspecting-ship "Beskytteren", C. \'. Utterstrom 1903, K.J. Gemzoe 1904, and F. Johansen 

 1905 (Iceland). 



"Thor", fisheries-investigations 1903, 1904, 1905, 1906, and 1908 (British Isles, Norway, Faeroe 

 Lslands, Iceland). 



"Tjalfe", 1908 and 1909 (West-Greenland) 



"Armauer-Hansen", Norwegian research motorship, 1913 (West of Rockall). 



The state of preservation of the material has partly been very satisfactory (formalin), parti- 

 cularly as far as the collections of the "Thor" and the "Tjalfe" are concerned. The material of the 

 "Diana" is likewise generally well preserved, though it has only been treated with alcohol; the same 

 testimony is partly applicable to the material from the "Beskytteren" collected by Gemz0e. The 

 material from the "Ingolf Expedition, on the other hand, is as a rule very badly preserved. Especially 

 a great lot of .specimens have been spoiled owing to the usage of osmic acid or Flemmings solution. As 

 a matter of fact, these substances have quite a ruinous effect on medusae, particularly so if the dis- 

 solution is too concentrated and the specimens are exposed to the influence of the fluid during a too 

 long space of time. Not merely the pigmentation is concealed, but the animals become intransparent 

 and very much fragile, and must be handled with the utmost care not to break during the examina- 

 tion. Indeed, still during the transportation in the glasses a great part of the material has been shaken 

 into small fragments. Neither are the single organs better hardened for investigation by this method of 

 preparation; I have tried sectioning on microtome different organs of specimens treated with Flemmings 

 solution, and the tissues are by no means better preserved, rather more badly if anything, than in the 

 case of animals merely preserved in common alcohol or formalin. The method of treating medusa; 

 with fluids containing osmic acid .seems to have been very favourite during a certain period: on account 



