LIMNOLOGICAL PROBLEMS 
423 
The new conditions which the temperate zone after the end of the 
Glacial Age offered its organisms have, on the other hand, also acted 
long enough to leave their mark on structure and mode of life. Such 
marks are the variation, local as well as seasonal, both of which are 
nothing but the efforts of the organisms to adapt themselves to the 
development of more favourable biological conditions consequent 
upon the milder climatic conditions. The differentiation in the 
outer conditions involved differentiation in structure. 
How have these extensive researches on the variation in the Northern 
and Central Kuro^ean fresh-water planMori influenced onr conception 
of the species We must in this paper be content to deal mainly 
with the Cladocera and leave the remainder to the future. 
I have here come to the point which is the goal of so many other 
comprehensive studies. I confess openly that I have held conflicting 
views at different times, but I believe that the result which I have 
arrived at lately is for me permanent. HoAvever honest and sincere 
one's researches may be, and however much one tries to be impartial, 
in such domains one is, in my opinion, only able to see what one is 
" born to see, i.e. the combination of claims and conditions which 
is the reflection of one's self. I consider it highly probable that if 
other observers with other natural gifts had procured the material 
shown here and had now to say the final word, they would express it 
differently from what I should. Man cannot, on the whole, get 
beyond what he thinks is the nearest truth. 
According to my view, the researches clearly show the almost 
incredible elasticity of the plankton organisms and their adaptability 
to variations in outer conditions. For many extremely different 
organisms the research has more or less distinctly shown that a 
transformation takes place in the shape of the organisms, which is 
uniform in its final results and everywhere parallel with certain fixed 
local and seasonal variations in outer conditions. This harmony 
between the variations in outer conditions and those in the shape of the 
plankton organisms is, in my opinion., so conspicuous that I do not doubt 
but that the latter are the outcome of the former. It seems to me 
that but few researches have been able to display so clearly the 
influence of outer conditions on the organisms ; but even with 
regard to this point the mere subjective view cannot, as above noted, 
be excluded. According to my opinion, the salient point is that the 
research has proved the causal connection between the shape or form 
of the plankton organisms and certain regular variations in outer 
conditions. Which of the two really " strikes the first blow " in the 
mutual play between organism and outer conditions, whether the 
organism is forced or permits itself to be forced, is in my opinion a 
contest of words, and provisionally may be left alone. Through this 
