THE ROTIFERA OF THE SCOTTISH LOCHS. 159 
Diglena, Diaschiza, Diurella, Philodina, and Callidina. These genera constitute the 
characteristic Rotifer-fauna of lake-margins; other genera, though common enough, 
are more casual in their occurrence. There are several species of each of these genera 
commion in the littoral region, though none of them are confined to lakes. 
It is in the littoral region that the richest Rotifer-fauna is found ; in fact, the whole 
Rotifer population of a lake may be ascertained from the marginal collections, as the 
limnetic and the abyssal species here meet and mingle with the proper littoral forms. 
Including the casual as well as the permanent inhabitants, a large number may occur 
in any one lake. We observed 148 species in Loch Ness—undoubtedly far under the 
true number—and Srenroos noted 157 in Nurmijirvi-See. 
From sixty to eighty of these species may be considered as of ordinary occurrence 
in lakes, and likely to be found in any lake which is carefully examined. The others 
are more local and uncertain. 
Although by far the most densely peopled part of the lake, the littoral region has 
not the most marked lacustrine character. It is the few limnetic species which are 
most truly characteristic of lakes. Although the limnetice Rotifers also occur in ponds, 
their special characteristics are such as fit them for lake life. These characteristics— 
spines, transparency, free-swimming, ete.—have probably had their full development in 
lakes, though the animals now often extend into smaller waters. 
The littoral Rotifers are none of them confined to lakes; they may be found in 
moist places anywhere—in ponds, bogs, streams, and among moss. Nevertheless, even 
the littoral region has a certain lacustrine character. 
Leaving out of account some very shallow lochs and certain bodies of contaminated 
water near towns, the water of our lochs is, on the whole, pure, if peaty, and the 
genera given above as most common in lakes are those which have a preference for 
clear water. 
A small number of species may be cited as pre-eminently characteristic of pure lakes, 
though not exclusively lacustrine. Most of them are Bdelloids. They are Microdina 
paradoxa, Philodina fllawiceps, P. brevipes, Furcularia reinhardt, and Euchlanis lyra. 
The shallow, weedy bays of the larger lochs, such as Inchnacardoch Bay in Loch 
Ness, afford much the same breeding-grounds for Rotifers as ponds and bogs, and it 
is in such bays that most of the casual species occur. Here we find swamp Rotifers, 
Rotifers from streams, and moss-dwellers casually introduced, all flourishing together. 
There is one important distinction between such bays and ponds or swamps, which 
probably accounts for the number of casual species being smaller than might be 
expected. So long as these bays are in open communication with the deep water of 
the lake, a moderate temperature is maintained. Inchnacardoch Bay was never more 
than a trifling degree warmer than the centre of Loch Ness. 
The distinction drawn by Jennies (26) between swamp and lake Rotifers is as 
clearly marked here, when such bays become in dry seasons completely cut off from the 
loch. Such a case is found in an extensive swampy stretch in Burlom Bay, Loch Ness. 
TRANS. ROY. SOC. EDIN., VOL. XLV. PART I. (NO. 7). = 
