154 MR JAMES MURRAY ON 
XOUSSELET, 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 
aelly 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. 
Petacic REGION. 
It has been truly remarked by Dr C. Wesenpera Lunp (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 Synchxvta 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 limnetie of all Rotifers, Notholea 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 merease 
for a time ina small loch. In a little loch in Galloway (Loch of Cults), one of the most 
abundant animals in the plankton was Polychetus collinsii (Goss). 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 limnetie Rotifera is the simple one of drawing tow-nets 
