LIMNOLOGICAL PROBLEMS 
375 
the physical and chemical conditions of the lakes of the tropics is 
extremely slight. What I have tried to do in the following, with 
regard to the Arctic, North European, Central European lakes of the 
level country (Baltic lakes) and the alpine lakes, has been to bring 
together the available information concerning the topography and 
general geography of the lakes : morphometry, bathymetry, littoral 
region with littoral vegetation, character of the soil in the drainage 
area, precipitation, temperature, chemistry, colour, and transparency 
of the lake-water. In Part 11. I have tried to give a sketch of the 
plankton communities, their geography and life-history; and in Part 
III., according to Sir John Murray's special wishes, to expose my views 
with regard to the main problems of future limnological investigation. 
PART I.— CONTRIBUTION TO THE GENERAL GEOGRAPHY 
OF THE LAKES 
The Arctic Lakes 
If we try to form a picture of the arctic lakes, we have unfortunately 
but few certain facts to rely upon. It is only by means of general 
descriptions of the nature of the arctic regions that a vague and 
uncertain sketch, which must be corrected and added to in future, 
can be given. During the last ten years I have read many accounts 
of travels in the arctic regions, hoping to find accounts of arctic lakes. 
From tliis literature I shall attempt to give an outline of the nature 
of arctic lakes and the conditions of life which they offer their 
organisms. 
The rainfall is stored as large snow and ice-masses, of which 
but a small part, and that only for a short period of the year, breaks 
forth from the ice into the lake-basins in the form of torrential rivers. 
The country surroiuid'mg the lakes is perpetual snow, naked rock 
or sparingly coated (moss-covered) rocky slopes, sometimes wide 
tundras frozen throughout the whole or at any rate the greater part 
of the year. 
No account of the sizes and depths of arctic lakes on which to 
found a general description is available. The descriptions of travellers 
convey the general impression that the arctic lakes are comparatively 
small. In the real lakes the littoral zone is always narrow, the pelagic 
region reaching up to the shore. The primary lake bottom is rock 
or rough sand and gravel. The height of the water will undergo 
considerable variations : high water in spring, low water in autumn. 
In lakes near the margin of the ice, where the affluents are rivers of 
cold water from the inland ice, the water is surcharged with par- 
ticles of clay. The filling up of the real lake-basins probably proceeds 
