THE FRESH-WATER LOCHS OF SCOTLAND. 
31 
amount of the organic life in the fresh-water lochs are subject to great 
variation in the different lochs when compared with each other, and in 
the same loch at different seasons of the year. Large numbers of 
observations are being collected, and we may look for interesting results 
when these are in a state for discussion. Generally speaking, the 
pelagic fauna and flora are much more abundant in the warm summer 
months than at other times of the year, and are also more abundant in 
the shallow lochs than in the deep ones. In the spring months there is 
a great development of diatoms and other Phytoplankton, which render 
the water less transparent than at other times of the year. 
Mr. Thomas Scott has lately been comparing the fauna in several of 
the Scottish lochs at different seasons of the year; some of his results 
for the lochs now under consideration may be noted. 
In Loch Katrine the Entomostraca and other invertebrates were 
scarcer than in the other lochs examined. Fourteen species are recorded, 
Bosmina longis'pina being the only species present in all the gatherings ; 
Leptodora was entirely absent from the gatherings collected during the 
colder months, Cyclops strenuus and Polyphemus appeared to be more 
frequent in the upper part of the loch, and Bosmina and Leptodora in 
the lower part. The sides of Loch Katrine do not generally present 
conditions very favourable to shore-dwellers, and an examination of the 
shore about Stronachlachar yielded scarcely anything that differed from 
the tow-net captures, while at the lower end the shore between the 
Trossachs pier and Ellen’s isle yielded much better results. Here forty 
species of Crustacea were obtained, as well as one or two species of 
Mollusca, but they were all individually scarce. The Cladocera were 
more numerous in species in the warmer than in the colder months, 
while with the Copepoda the reverse was observed, though the difference 
was not so great.* 
In Loch Arklet, Holopedium gihherum, one of the most remarkable 
species of the Cladocera in Britain, was moderately common in the 
tow-net gatherings collected in September and November, 1897, and in 
June, 1898, it was abundant all through the water, but when the loch 
was visited in March, 1898, not a trace of Holopedium could be seen. 
In June, when Holopedium was so abundant, other species previously 
observed were either very scarce or absent, as if they had been more 
or less crowded out by this particular cladoceran. Eleven crustacean 
species are recorded, Day^hnia being the only form obtained in all the 
gatherings; Bythotreidies was observed in September and June, but not 
in November and March, and Leptodora occurred only in September. 
Infusoria (Geratium, &c.) and micro-algse were much less frequent in 
June than in the other gatherings. Forty-two species of Entomostraca 
were obtained by hand-net round the shores of Loch Arklet, including 
* Scott, Seventeenth Annual Report of the Fishery Board Jor Scotland^ pt. iii. pp. 148-151, 1899. 
