412 Proceedings of Eoyal Society of Edinburgh. [sess 
II. 
The Organisms, and their Relations to the different 
Life-conditions, in the Danish and Scottish Lakes. 
It will be easily understood that the life-conditions offered to 
fresh-water organisms differ widely in the Danish and Scottish 
lakes respectively, and that there are great differences between 
the vegetable and animal life in each case. Generally speaking, 
it may be said that the low temperature and freezing over of the 
Danish lakes in winter have not hindered the immigration of 
most of the fresh-water organisms distributed over the entire 
temperate region of Europe, while the usually high summer 
temperature, due to the shallowness of our lakes, is undoubtedly 
one of the main factors to which we must ascribe the extremely 
rich organic life, both as to the number of species and of indi- 
viduals, characteristic of our own as well as most of the lakes in 
the northern part of the Central European plain. We shall now 
consider the vegetable and animal life in the Danish and Scottish 
lakes respectively, according to the three main regions that may 
be recognised in every lake, viz., the Littoral region, the Pelagic 
region, and the Abyssal region. As far as possible, we shall 
endeavour to indicate how the different characters of the lakes in 
the two countries have produced great differences in their 
associations of animals and plants. 
A. The Danish Lakes. 
1. The Littoral Region . — Owing to the gently sloping shores, 
the smooth wash of the waves, the sandy beaches, often covered 
with decaying vegetable matter, and the high summer temperature 
of the coastal waters, most of our lakes are bordered by dense and 
luxurious bands of vegetation, which in shallow bays may attain 
a considerable width, merging imperceptibly into the vegetation 
of the adjoining land. Thus our lakes are often in certain parts 
bordered by humid meadows, which in winter and spring are 
covered by ice or water, while in hot summers they may be quite 
dry, so that it is frequently difficult to say where the land ends 
and the lake begins. 
