Copepod Fauna of the “‘Maare” of the Eifel. 299 
maar ’’ into a comparatively large basin, while as regards the 
small D. graciloides, Lilljeborg’s statements, according to 
which it particularly affects large pieces of water, are con- 
firmed. 
As no doubt in most cases, all the waters in the district of 
the Eifel have probably been peopled with Copepoda by 
passive immigration. Moreover active immigration could only 
occur in those lakes which are connected with the river- 
system of the Moselle and Rhine, e. g. in the Laacher See. 
I think, however, that we may assume with good reason that 
the lake just mentioned owes its richness in species to the 
greater concourse of aquatic birds and insects induced by its 
more extensive surface. These, according to Migula’s recent 
investigations *, evidently play a most important part in the 
peopling of closed basins with the lower animals. ‘The com- 
pletely closed Gemiinder Maar obtained its Copepod fauna, 
which nevertheless is considerable, solely by such transporta- 
tion. 
From the results obtained it seems very desirable that 
those “ Maare” which have not yet been investigated should 
be carefully studied. Those which have already been 
examined will also furnish much of interest to renewed 
investigation, perhaps at different seasons of the year. IHven 
the remarkable circumstance that in most ‘ Maare” at the 
season apparently most favourable for the reproduction of the 
Copepoda so few animals with mature sexual products were 
found is an inducement to further investigation. 
On a Cyclops with a defective Furca. 
In my repeated examination of the Copepod material from 
the Laacher See my attention was attracted by a specimen of 
Cyclops agilis, Koch, of which the furca was crippled in a 
remarkable manner. ‘he right half of the furca is thinner 
and about one fifth shorter than the left half. Curiously 
enough the sete are as strongly developed on the smaller 
member as on the normal one; only the outer apical seta is 
removed to the place which in the normal form is occupied 
by the outer lateral seta. ‘The latter, in the right division of 
the furca, is seated nearly in the middle of the outer surface, 
and is therefore displaced towards the head. Further devia- 
tions from the normal structure are also shown by the last 
three abdominal segments, inasmuch as they do not lie straight 
behind one another, but form a slight curve towards the right. 
* ‘ Biologisches Centralblatt, 1888, no. 17. 
