154 MR JAMES MURRAY ON 



ROUSSELET, who have at all times been courteously willing to examine drawings and 

 materials sent to them, and to give me the advantage of their judgment as to the 

 value of species. I desire here to express my sense of the obligation they have 

 conferred upon the Lake Survey. The Rotifers recorded for Loch Leven and Loch 

 Gellv were collected by Mr Evans and identified by us. 



In common with other groups of lacustrine animals, the Rotifera can be most con- 

 veniently studied by treating separately the species inhabiting each region of the lake — 

 the pelagic region, the littoral region, and the abyssal region. The association of species 

 constituting the plankton is very distinct, but of limited number : the littoral region 

 is very rich ; the abyssal, if it can be said to exist at all in Scotland, is very thinly 

 populated, and distinguished by negative characters only. 



Throughout the text, references to the bibliographical list at the end of the paper 

 are made by figures in heavy type, enclosed in parentheses. 



Pelagic Region. 



It has been truly remarked by Dr C. Wesenberg Lund (34) that the Rotifera on 

 the whole play but an inconspicuous part in the pelagic region of the larger lakes. 

 The Scottish lakes form no exception to the rule. Nevertheless, the Rotifera must be 

 accorded the second place in importance in the limnetic fauna, as, after the Crustacea, no 

 class of animals except the Rotifera is habitually represented by several species in most, 

 if not all, lakes. The number of species in each lake is small, and, as they are such 

 minute animals, they must become exceedingly numerous before they can be conspicuous 

 in the plankton. 



Frequently in the smaller lochs, and perhaps occasionally in the larger ones also, 

 though no instance of it has come under my notice in Scotland, one or more species will 

 so increase as to be for the time being more conspicuous than any other organism in 

 the lake. Species of Synchseta and Asplanchna, which are giants of their class, most 

 frequently do this. In a little hill loch (L. Breachlaich) near Killin, in the early 

 summer of 1903, Asplanchna priodonta was so abundant as to obscure all other life in 

 the loch. After drawing our nets for the usual five minutes, a whitish slime filled the 

 bottom of them, consisting solely of this animal. In a very small loch (Monk Myre) 

 near Blairgowrie, the most truly limnetic of all Rotifers, Notholca longispina, coloured 

 the collection (five minutes' tow-netting in a two-ounce bottle) dark red, and little else 

 could be seen. 



Sometimes a species, not usually regarded as truly limnetic, will greatly increase 

 for a time in a small loch. In a little loch in Galloway (Loch of Cults), one of the most 

 abundant animals in the plankton was Polychsetus collinsii (Gosse). This phenomenon 

 might conceivably occur in our great lakes, but has not been observed, and such 

 swarming is probably prevented in them by the always moderate temperature. 



The method of collecting the limnetic Rotifera is the simple one of drawing tow-nets 



