LTMNOLOGICAL PROBLEMS 
429 
of exploration at present expend. It must be remembered that such 
observations in Scotland, in the great Swedish lakes, in the Baltic 
lakes, and in the Lake of Geneva, as well as in many of the American 
lakes, may be connected with investigations already being carried out, 
and by investigators who at these places have already studied the 
very same phenomena. In all these localities the investigations will 
be relatively cheap : neither money nor the right men would be 
difficult to get. The great difficulties arise only in the case of the 
arctic and tropical lakes, and, as far as I can see, especially the 
latter. Here it is probably necessary to restrict the demands, and 
to remember that it is not altogether necessary that the scientists 
should live during the whole year at the locality ; they might leave 
the plankton collecting and temperature observations to men who 
during the stay had been trained for that purpose. The material 
collected should be given into the hands of a committee, who should 
determine its further elaboration. Sooner or later this plan will 
undoubtedly be carried out. Whether the present is the right 
moment, I do not know ; but I do not see why it should not be. 
Whilst pointing out what, in my opinion, is most needed to 
promote limnology, I wish at the same time to indicate briefly the 
lines which, in the present position of the science, may be regarded as 
already worked out. When the plankton investigations began, very 
many small papers relating to the pelagic fauna or flora of fresh water 
appeared. Many of these papers were the result of a single excursion, 
and the plants and animals were cursorily determined. Papers of this 
kind are now indeed rare, but they have by no means quite disappeared. 
It must be strongly emphasised that all papers of this kind, if they 
are only the result of a single excursion and the collection only 
contains common forms, are of exceedingly little scientific use. This 
holds good especially for the material obtained from the temperate 
zone. For example, no scientist who has made an excursion in a 
stretch of woodland thinks of communicating to the scientific world 
that he has found violets and wild flowers; but just as unnecessary 
is it to conniiunicate that one of the thousands of Baltic lakes is 
populated with D. hyalina, Polyarthra platyptera^ and other cosmo- 
politan species. Publications of this kind should no longer be printed 
in scientific periodicals. 
During the last ten years we have obtained from different 
countries a number of lake descriptions ; they belong almost all to 
the temperate zone, principally to the Baltic or Swiss lakes. We 
find in these papers a pot-pourri of very many different branches of 
natural science : physics, chemistry, geology, meteorology, zoology, 
botany, all treated and finished off' in one or two hundred pages. 
The starting-point for these publications is that a lake is a sharply 
