1132 Proceedings of Royal Society of Edinburgh. [sess. 
Among the cosmopolitan stock of plankton Rotifers from greater 
lakes, I also reckon Anurcea aculeata and Triarthra longiseta, 
which have not been found in Thingvallavatn. This stock then 
consists of the following species : Polyarthra platyptera , SyncJiceta 
sp., Asplanchna priodonta , Anurcea cochlearis, Anurcea aculeata , 
Notholca longispina, Conochilus unicornis , and Triarthra longiseta. 
Skorikow (1904, p. 209) has pointed out that all the species 
from the lakes on Kolgujev have also been found in the alpine 
lakes of Switzerland. Skorikow’s point of view in this regard is 
expressed as follows (p. 212): “Ein Ubereinstimmen der ark- 
tischen und alpinen Fauna ist gewiss nichts Neues, aber eine so 
vollstandige Identitat wie in diesem Falle, meine ich, verdient 
einige Aufmerksamkeit ; besonders ist dies hinsichtlich der Rota- 
torien interessant weil man sie in schon iibertriebenen Mass 
als untauglich fur geographische Z we eke ansah.” 
According to my opinion, Skorikow takes a wrong view of the 
result of the exploration. Nowadays we have found in every 
thoroughly explored lake with a well-defined limnetic region the 
above-mentioned stock of Rotifers ; it belongs by no means only 
to the arctic and alpine lakes, but quite as well to all lakes 
situated between the arctic and the central European highlands. 
So that when we may show “vollstandige Identitat” in the 
plankton Rotifers of the arctic and the alpine lakes, this is, geo- 
graphically speaking, by no means noteworthy ; on the other hand, 
and from a biological point of view, it becomes of interest 
that the association of Rotifers living under arctic conditions 
remains the same everywhere ; in the shallower, and in summer 
much warmer, lowland lakes this association also exists, but is 
here mixed up with all the monocyclic summer Rotifers which, in 
order to exist, require a tp. of between 16° and 20° C. 
It may be that the Rotifers at some future time may become 
instrumental in furthering geographical studies far beyond those 
we at present dream of. Still, I feel convinced that the way in 
which so many naturalists, from observations based upon a few 
samples collected in out-of-the-way places of the globe, often think 
fit to lay down laws for the distribution of the associations, or to 
subvert results that have been arrived at by others, is not much 
to the purpose. 
