428 THE FRESH-WATER LOCHS OF SCOTLAND 
Wetter, Ladoga, Loch Katrine, Lake of Geneva, has been pubhshed ; 
still, temperature observations in the tropical lakes are wanting, and 
those for the arctic lakes are unsatisfactory. The investigations made 
are, as a first attempt, of great interest, but they by no means exclude 
the necessity for further observations. If such simultaneous tempera- 
ture investigations could be combined with limnographical and chemical 
researches at different latitudes, we should in a couple of years be able 
to get wide fundamental views which all researches in these vast fields 
of labour at this moment lack. 
In the foregoing we have dealt with the cosmopolitanism of the 
fresh-water organisms, especially that of the plankton. We can point 
out many species of plankton organisms which are just as much at 
home in the dark, ice-cold arctic lakes as in the hot tropical lakes ; 
e.g., amongst Rotifers we know about ten species, amongst Crustacea 
Daphnia Jiyalma, species of Bosmiria, among Diatoms the Melosiras. 
It is just with regard to these species that great differences in the 
views of their morphology and biology prevail. What is wanted 
here is regular fortnightly investigations carried out simultaneously 
in different latitudes. From these we should get a clearer understand- 
ing of the above-mentioned different uses of digonic and monogonic re- 
production in different latitudes ; we should get a much more thorough 
knowledge of the form-series of the plankton organisms, and un- 
doubtedly learn many more than those we now know (Diatoms, 
Desmids, Calanidae, Rotifera) ; from these investigations much material 
for the great (questions with regard to the origin of species might be 
gained. 
As is well known, the different North and Central European 
States have joined in the great scientific co-operation, the interna- 
tional exploration of the sea. A corresponding international limno- 
logical exploration needs neither such great apparatus nor the 
enormous sums which the exploration of the sea demands. All that 
is necessary is to have for a period of one or two years a few scientifi- 
cally educated men placed at six or seven localities arranged in almost 
the same longitude from the north to the equator. We should use 
one or two places of observation in the arctic regions (Greenland and 
Lake Enare), in Scotland, and in the great Swedish lakes, in the Baltic 
lakes, in a high alpine lake, in the Lake of Geneva, and in the great 
African lakes. If a similar series of observations could be carried out 
in America, and if a station could be founded on the Baikal Lake, 
these would be of great use. To carry out this plan, neither great 
congresses nor many committee members or great sums granted by 
Governments are necessary, but only a very few scientists agreeing in 
the main points and with relatively modest funds, which in most cases 
will not exceed what scientific societies or bodies interested in this kind 
