160 MR JAMES MURRAY ON 
When the level of Loch Ness is high this forms a mere bay, having the temperature of 
the rest of the lake, and all the usual lacustrine animals. In summer it is quite cut off 
from the loch, becomes greatly heated, and has a stagnant-water fauna distinct from 
that of the lake. 
The littoral Rotifera in Loch Ness had a very distinct winter maximum develop- 
ment. They began to be abundant in December, reached the maximum in February, 
after which there was a steady and great decline. Many species, notably Cathypna 
ligona, were only seen during the few winter months; others were in the loch all the 
year round, but increased greatly in numbers in winter. This cycle was traced during 
two seasons, 
ABYSSAL REGION. 
As I have already pointed out (40), the limited researches made by the Lake Survey 
have not revealed in the Scottish lochs any peculiar abyssal organisms whatever, except 
some Rhizopods which Dr PrNnarp regards as peculiar to great lakes (41, 42). 
Many Rotifers do, however, extend from the littoral region into what would else- 
where be designated the abyssal region—although that term has no biological significance 
with us, in the sense in which Foret uses it (14). 
Our knowledge of the vertical range of the littoral Rotifers is based on observations 
in Loch Ness. There alone have our studies been carried on for a suficiently long time 
to justify us in supposing that we have a fairly adequate knowledge of the life of the 
abyssal region. A few species have been got in the mud of other lochs (7.c. Loch 
Rannoch, Loch Oich) at moderate depths. In Loch Ness, dredgings have been made 
with sufficiently fine nets at all depths down to 700 feet, and often enough to lead us 
to suppose that if Rotifers were abundant we would have found them. Rotifers were 
abundant at depths of less than 100 feet. Beyond that depth they became rarer as 
the depth increased, down to 300 feet, after which they dropped out altogether: only 
on one occasion was a single species, Proales daphuicola, found parasitic upon 
a worm at 500 feet. Between 250 feet and 300 feet the fine net on several occasions 
brought up numerous Rotifers, of about twenty species. Dredgings at those depths 
were unequal, often containing no Rotifers at all. All the Rotifers were of common 
littoral species. As it is of some interest to know what species are most capable of 
adapting themselves to varying conditions of light, temperature, pressure, ete., the 
complete list is given of all the species found at depths exceeding 250 feet :— 
Philodina macrostyla, and the form Monostyla lunaris. 
tuberculata. Dinocharis tetractis. 
Hosphora najas. Metopidia acuminata. 
s digitata. ; solidus. 
Diglena uncinata. “fi triptera. 
Diurella tenuior. 5 oxysternum. 
Diaschiza tenuior, Coiurus obtusus. 
Euchlanis deflexa. Proales daphuicola. 
> lyra. 
