BIOLOGY OF TBE SCOTTISH LOCHS 
285 
the shallow Continental lakes. Even so far north as Denmark the 
annual range seems to be about 10°'0 Fahr. greater; in the great 
Balatonsee of Hungary it is much higher — nearly SO^'-O Fahr. The 
greater range of temperature will favour seasonal variation. The 
higher summer temperature will be likely to encourage a richer fauna 
and flora ; the low winter temperature will be unfavourable to life. 
An exceptionally severe winter may cause some of the smaller lochs 
of the first class to be for a time transferred to the second. 
We are not in a position to trace the actual relation of the life- 
changes throughout the year to the changes of temperature, except 
in the case of Loch Ness, which may be taken as a fair type of the 
first class. That loch was examined regularly for more than a 
complete year. Loch Morar has been examined at all seasons, but 
irregularly and at long intervals. Several lochs which freeze in winter 
have been examined in midsummer and in midwinter. 
In the great lakes which never freeze there is no very marked decrease 
in the quantity of organisms in winter. Many of the species persist 
all the year round ; but as those which are absent in winter are the 
most conspicuous of the Crustacea, the difference between the winter 
and the summer plankton appears rather striking. Holopedknn^ 
Polyphemus^ Bytliotrephes^ and Leptodora are all absent during a part 
of the year. 
Cos7nopolitan Element m the Plankton. — For information as to 
the general plankton of Europe and other regions I am mainly 
indebted to various papers by Dr Wesenberg-Lund, who has made 
wider comparative studies of plankton. 
Only those species which are generally distributed over Scotland 
can be taken into account in comparing the plankton of Scotland 
with that of Europe generally. The animals M^hich are dominant or 
common both in Scotland and the rest of Europe are : Diaptomus 
gracilis^ Daphnia hyalina., Diaphanosoma hraehyurum^ Leptodora 
kindti% Conochilus unicornis^ AsplancJina priodo7ita^ Polyarthra 
platyptera^ Anuraa cochlearis^ Notholca longispina^ Ceratknn hirim- 
dinella^ and Asterionella. 
All of these, according to Dr Wesenberg-Lund, belong to the 
general plankton association of the great European plain, or are 
even cosmopolitan. 
Peculiarities of the Scottish Plankton 
The Scottish plankton differs from the plankton of the. Central 
European plain and from the cosmopolitan fresh-water plankton 
in several respects. The most striking peculiarity is the extraordinary 
richness of the phytoplankton in species of Desmids, shared only, in 
