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 

 peophng of closed basins v.'ith 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. Even 

 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 agiiis, Koch, of which the furca was crippled in a 

 remarkable manner. The right half of the furca is thinner 

 and about one fifth shorter than the left half. Curiously 

 enough the setse 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 anothei", but form a slight curve towards the right. 



* ' Biologisches Centralblatt/ 1888, uo. 17. 



