SOME ROTIPERA FROM SPITSBERGEN. 307 



among the 51 forms, 34 Bdelloida and 6 Ploima are species 

 wMcli are rarely or never met with except where moss is 

 present ; while 1 Bdelloid, 8 Ploima and 1 Floscularian are 

 species almost invariably found in pools or deeper waters. The 

 presence of these 10 species in the mosses examined is doubtless 

 to some extent accidental. 



At least 70 of the 81 forms enumerated in the full list given 

 later have not only been already found in the more temperate 

 countries of Europe, but are actually more or less common in 

 Great Britain itself ; among the species described as new there 

 are no startling variations from already known European 

 species. Thus, so far as they are yet known, the Rotifera of 

 Spitsbergen furnish absolutely no evidence of local evolution. 

 In this connection I may add that a very similar position is 

 shown in the recently published report by Harring (4) on the 

 general plankton collections made by the Southern party of the 

 Canadian Arctic Expedition 1913-1918, which deals with pond 

 or lake-dwelling rotifers only. These plankton collections, made, 

 as I understand, in the north of Alaska, yielded in all 64 species 

 of Rotifera, of which 5 are new to science. Of the remaining 59 

 species, no less than 50 are to be found in Great Britain and 

 most of them are quite common forms. Although dealing for 

 the most part with quite a difierent set of species, Harring's 

 list tells much the same tale as does mine, viz. that these species 

 from the far north are practically identical with those living 

 in more temperate countries. It is the nature of the actual 

 habitat, especially as regards the plenteous provision of suitable 

 food, that is the predominant factor in the distribution of 

 Rotifera, and temperature, if not too extreme, has only a 

 secondary influence. 



I think, however, that extremes of temperature may in some 

 cases exercise a distinct influence upon the distribution of 

 Rotifera, and that this is shown by Murray's (6) experiences in 

 the Antarctic. Shortly after he had completed his report on Dr. 

 Bruce' s collections of mosses from Arctic territories, Murray 

 became biologist to the British Antarctic Expedition, 1907-1909, 

 and investigated the rotifer-fauna of the district near Cape 

 Royds, where the expedition had its base for two summers and 

 the intervening winter. His previous extensive knowledge of 

 Rotifera, whether moss- dwelling or pool- dwelling, peculiarly 



