16n Canadian Arctic Expedition, 1913-18 



America are fairly well known, thanks to the southward extension of subarctic 

 temperatures to New England. 



Judging from what is known of the distribution of Medusae in arctic waters 

 and, indeed, of most other marine organisms, no great faunal peculiarities, dis- 

 tinguishing the regions studied by the Canadian Arctic Expedition from Bering 

 sea on the one hand, or from the coasts of Labrador, Greenland, or Spit/bcrgi-n 

 on the other, were to be expected, the general thesis of the circumpolarity 

 of most littoral arctic organisms being well established. And, as a matter of 

 fact, none is shown by the collection, all the Medusae and Ctenophores taken by 

 the Canadian Arctic Expedition north of Bering straits belonging to species well 

 known either from some part of the North Atlantic or from its arctic tributaries, 

 except for the one new species (p. 7n). Such are Sarsia princeps, Sarsia flammea, 

 Rathkea blumenbachii, Halitholus cirratus, Aglantha digitale, Aeginopsis laurentii, 

 Chrysaora sp., Cyanea capillata, Mertensia ovum, Beroe cucumis, and Bolinopsis 

 sp. All of them were living under purely Arctic conditions of temperature, 

 often, as noted by Mr. Johansen, in the leads and openings in the ice and under 

 it. And judging from the geographical location of capture, there is no reason 

 to suppose that any of them are other than endemic to the Arctic ocean, some- 

 thing which cannot always be said of collections from Spitzbergen, or from 

 Barents sea. Thus, to take an example, for Chrysaora to have reached Dolphin 

 and Union strait as an involuntary immigrant from either North Atlantic or 

 North Pacific waters would require a drift of not less than 1,000 miles; neces- 

 sarily carried out since the Medusa was set free (Chrysaora passes through a 

 fixed stage), which, to judge by what is known of the rate of growth of th.e large 

 Scyphomedusae in cold waters, probably took place not more than three months 

 prior to its capture. Similarly, it is perfectly safe to conclude that the several 

 Hydroid Medusae which are evidently common at Collinson point, are normally 

 at home there. It does not follow, however, that all of them are restricted to 

 waters of arctic temperature, in their normal distribution. On the contrary, 

 it is well established that Cyanea capillata among Scyphomedusae, Halitholus 

 cirratus, Rathkea blumenbachii, and one or another variety of Aglantha digitale 

 are equally endemic in the boreal waters of the North Atlantic. 



It is of great importance, not only to the students of the group, but especially 

 to the oceanographer, to establish definitely which of the Arctic Medusae are 

 certainly the products of arctic seas, and of them alone, for such natural buoys 

 are often of the greatest assistance in indicating the origin, northern or southern, 

 of the constituent waters of ocean currents. And they have the advantage 

 over the arctic diatoms, of large size and easy identification. Fortunately 

 there is at least one Anthomedusa, Sarsia princeps, which has been recorded 

 from so many parts of the arctic and from the currents flowing from it, e.g., 

 the Labrador current, but no where else, that it can safely be taken as a sure 

 indication of arctic water. Wherever it may drift, it can be as surely retraced 

 to an arctic home as can a Nova Scotia coast buoy which has strayed out into 

 the Gulf Stream, to coastal moorings. And no better natural buoy could be 

 found for not only is its arctic origin certain, and its drift period limited (by the 

 fixed hydroid stage), but it is so large and its specific features so characteristic 

 that the veriest tyro could be trusted to recognise it from a good drawing. S. 

 flammea would perhaps be an equally safe index to arctic waters, except that it 

 is less distinguishable from its relatives. 



Among Leptomedusae I may mention, as an arctic index, Ptychogena lactea 

 (not, however, represented in the present collection). Typically arctic Tra- 

 chomedusae are Ptychogastria polaris (1909b, 1913.) and Botrynema elinorce (Hart- 

 laub, 1909; Bigelow, 1913, p. 52). 1 



MSince Ptychogastria polaris lives, as a rule, on or close to the bottom, and often in enclosed 

 waters, it is less apt to be of service to the oceanographer than the surface forms. 



