276 THE FRESH-WATER LOCHS OF SCOTLAND 
— are of little importance in connection with lakes. In the Inver- 
tebrata, on the other hand, there was a vast field, very partially 
explored in this country, the chief work having been done on the 
Crustacea by Dr Scott. The Phanerogamia and higher Cryptogamia 
were only studied by the Lake Survey in a few districts ; but the 
microscopic Algae, occurring in the plankton, were important in all 
the collections. 
lu this first part of the paper the biology of the different 
parts of the lakes is first studied — ^the open water, the margin, the 
bottom — then the distribution, origin, etc. In the " Census of 
Species'" given in Part IL, only those lochs are taken into account 
which were bathymetrically surveyed, in order that the biological 
report may strictly correspond with the bathy metrical. A bio- 
logical examination was made of many lochs not otherwise surveyed, 
and some interesting facts thereby added to our knowledge ; but such 
facts will not be treated of here. 
The distribution of some 700 species through more than 400 lochs 
offers difficulties in regard to its presentation in useful and convenient 
form. To give it in tabular form would need a large number of tables. 
While some of the plankton species have been found in nearly every 
loch, other species have been found in only one or two, or at any rate 
in very few lochs. There is no reason to believe that most of these 
latter are really more restricted in their distribution than the others. 
Many lochs may have been visited when those species were not in 
season ; but the main reason for the inequalities in the number of 
records for different species is that the margins of the lakes, whei e 
the major part of the life resides, could only be examined in a few 
instances. The distribution might be more concisely tabulated by 
grouping the lochs into districts, but even thus the records would be 
so very inadequate and unequal as to be actually misleading, and it is 
doubtful if such tables would serve any good purpose. There are, 
of course, some species which are believed to be really rare or 
restricted in distribution. Those which, though not rare, have well- 
marked limitations of range, will be treated in a special section on 
Distribution. Those which are rare or sporadic in occurrence will 
be referred to in the notes on the species which follow the list of 
species in each class. In this census it may be assumed that species 
not specially remarked upon in the notes are fairly generally distri- 
buted over the country. 
THE PLANKTON 
An understanding of the character of the plankton of the Scottish 
lochs may be obtained by considering, first, the features in which it 
