426 Proceedings of Royal Society of Edinburgh. [sess. 
abundant that it chokes up the nets in a short time, and makes 
it impossible to get a fair proportion of the other animals present ” 
(Murray, 1904a, p. 42); it may be added that the animals are 
extremely large. 
Df the genus Daph'nia the common species is Daphnia hyalin a 
in different varieties ( lacustris , galeata, etc.). D. (Hyalodaphnia) 
cucullata is very rare, and only found in one locality (a lowland 
lake). Bosmina coregoni is almost entirely absent, and it seems 
as though the genus Bosmina were only represented by one species, 
B. obtusirostris. Bythotrephes longimanus occurs generally in 
the Highland lakes, and is extremely large. Leptodora hindtii and 
Daphnella brachyura are common in nearly all the lakes. Of the 
Copepoda, the Diaptomidse are represented by D. gracilis , the com- 
monest species, as well as by D. laciniatus, D. laticeps , and the 
peculiar D. ivierzejskii ; of the Cyclops , C. strenuus is the main form. 
A s will readily be seen, the common occurrence of Leptodora 
hindtii and Daphnella brachyura is the only feature that gives 
the otherwise almost entirely sub-arctic association of Scottish 
plankton Crustacea a more southern facies. Otherwise we may 
point to a very close connection between the associations of 
plankton Crustacea in the Scottish and the sub-arctic lakes — a con- 
nection much closer than that between the plankton Crustacea of 
the Scottish lakes and of the lakes of the Central European plain 
and of Switzerland. This result is only what might have been 
expected, considering the situation of the Scottish lakes and the 
geological structure of the country, but still it seems to me not 
without interest. 
With regard to the other plankton-organisms, I shall only point 
out that Coretlira plumicornis has been found by Mr James 
Murray as a plankton-organism in Loch Oich, and that different 
species of Hydrachnids are common in most of the lakes. 
As regards the quantity of plankton in the Highland lakes, it 
can only be regarded as extremely poor when compared with that 
in the Danish lakes. It appears that the plankton in the larger 
Highland lakes affects the transparency or colour of the water only 
to a very slight extent, therefore the plankton can only slightly 
influence the general conditions of life for all the other organisms 
in these lakes. Only in small lakes has Mr' James Murray 
