121 
In gr. III Sida crystallina and Cyclops strenuus are lacking, whereas 
Lepidurus arcticus, which is lacking in gr. I and II, is found here. 
Though it is almost the same species which are occurring in 
the highland and in the lowland, the species do not occur with the 
same frequency. Some species are dominating in gr. 1, others in 
gr. II, and still others in gr. III (Tab. 4 and 5). 
Table 5 shows a similar variation with regard to the quantities 
of individuals, as Tab. 4 with regard to the frequency of occurrence. 
The two tables control and confirm each other. 
The difference, as regards the conditions of life between the 
highland and the lowland, is plainly expressed in the tables showing 
the distribution of the species. But the tables moreover show that 
though the conditions of life are changed, they are 
not (or only in a small degree) becoming worse. 
The species, which are dominating in gr. I, are either ubiquists 
(Chydorus sphæricus) or species with a more Southern distribution 
{Sida crystallina). The species dominating in gr. III have (with the 
exception of Daphnia pulex which is an ubiquist) a well marked nor- 
thcrn distribution. None of them are found in Europe south of the 
Alps, or in America south of the northern of the United States. 
The Distribution of the Species in Relation 
to the Vegetation. 
As it is shown in the lowest series of numbers in Tab. 6 and 7 
the number of species is increasing with the density 
of vegetation, and, with regard to the number of indi¬ 
viduals, the increase is even far greater. 
While it was not possible in the 3 groups of height, here dealt 
with, to show a deterioration in the conditions of life in accordance 
with the increasing heights, such a deterioration very distinctly fol- 
lows the diminishing density of vegetation. The reason why such a 
decrease takes place may be sought in this that the phytoplancton, 
which is in temperate countries a very rich source of food, is in 
the Arctic only very scarce. Thus the Entomostracians will here be 
reduced to live on the detritus, risen from the destruction of the 
higher plants, or on smaller animals feeding on detritus, and must 
consequently depend on the higher plants. 
