THE FRESH-WATER LOCHS OF SCOTLAND. 
141 
occasion do so. Asterionella, N otholca longispina, Asplanclina 
priodonta, Ceratium hirundinella, and even on one occasion the rather 
uncommon Rotifer Dinocliaris Gollinsii, have been observed to form a 
“ Wasserblut ” in the shallower lochs. 
The abundance of certain species in a loch on a single visit may be 
exceptional or temporary ; the small lochs may vary greatly at different 
seasons. It is believed that, except for the seasonal appearance of 
certain species which are known to live for only a few months of the 
year, a loch is pretty uniform in character throughout the year. This 
is known to be the case with the large lochs and with some small ones. 
The points to which attention will be called in reviewing the biology 
of the Tay lochs will be — the abundance or scarcity of life on the 
whole ; the preponderance of one or a few species in each loch ; the 
abundance of an animal or plant that is usually scarce; the absence 
or scarcity of some very common species. 
The lochs of the valley of the Earn differ much in size and physical 
conditions, so that they might be expected also to differ much in their 
biology. There is one great lake, Lodi Earn, two hill lochs, Turret 
and Uaine, the latter at a great elevation, one deep but stagnant pond, 
and one shallow artificial dam. 
Loch Earn. — The only abundant organism was Diaptomus gracilis, 
which was bright red in colour. There was almost no life at the 
surface, the Diaptomus being in myriads at a depth of 40 or 50 feet. 
The loch was rather remarkable for the scarcity of common lacustrine 
species. Bytliotreplies was somewhat frequent; Polyphemus, Cyclops 
strenuus, and Bosmina obtusirostris were present, but not plentiful, 
Daplinia was very rare, only one example being seen. Smaller 
organisms were almost entirely absent, except for a few examples of 
the two commonest pelagic Rotifers : Anurcea cochleare and N otholca 
longispina, and some unicellular Algae. 
Loch Turret. — This was one of the lochs where Holopedium filled 
the net with a slimy mass, and rendered it difficult to catch anything 
else. Diaptomus gracilis, Daphnia (typical D. lacustris), Asterionella, 
F eridinium tahulatum were noted. 
Loclian Uaine. — This little shallow tarn, in a corrie at a considerable 
elevation, had nothing remarkable in its pelagic life. Diaphanosoma 
hrachyurum was most numerous ; Diaptomus gracilis, of a brown colour, 
and Polyphemus were common. Only a few examples of Daphnia 
lacustris and Holopedium were seen. 
Loch Monzievaird (or Ochtertyre). — This loch, though fairly deep, 
was almost stagnant at the time it was visited. As might be expected 
from this and from the very high surface temperature, life was abundant 
and varied. The collection was green from the abundance of Yolvox. 
Bosmina cornuta, Daphnia lacustris, Diaptomus gracilis (of a brown 
