276 Dr. 0. E. Imhof on the Microscopic Fauna 



XXXIV. — On the Microscopic. Fauna of elevated Alpine Lakes 

 (600-2780 metres above the Sea). Bj Dr. 0. E. Imhof*. 



The geographical distribution of microscopic organisms pre- 

 sents a field in which persevering labour may ^till find a 

 fruitful soil. As microscopic animals are for the most part 

 inhabitants of the water, we must seek for our treasures espe- 

 cially in the larger and smaller water-basins. These we may 

 group as temporary and permanent. The former are accumu- 

 lations produced by great precipitations, which, however, 

 again disappear in dry weather. The others consist of tlie 

 persistent pools, ponds, lakes, and seas. Not only those of 

 the latter group, but also those of the former harbour animal 

 life during the time of their existence, and it is exactly in 

 this direction that comprehensive investigations are most 

 desirable, as these would show what animals survive the 

 period of desiccation either in the developed state or as ova, 

 what animals may be transported from one place to another 

 by atmospheric currents, &c. 



At present I leave out of consideration the geographical 

 distribution of the microscopic fauna in the seas, and confine 

 myself to the basins of fresh water. It may be mentioned in 

 passing that the microscopic fauna of the sea also presents a 

 fertile field of research, which has indeed only of late been 

 again investigated with some energy. The improvement of 

 the apparatus and of the methods of investigation are of 

 especial importance. I have had the opportunity of collecting 

 marine material by my improved methods, and always with 

 good results. Thus in materials from the Baltic a number 

 of microscopic organisms occurred the existence of which was 

 previously unknown. (Among vegetable structures Anaboena 

 and Asterionella.) Special value may be claimed for the 

 proof that in the Baltic forms of animals and plants occur 

 which are pretty generally distributed in our freshwater basins. 

 As examples, I may mention two of my new species of Fla- 

 gellata — Dinobryon divergens and D. elongatum. These two 

 forms also occur in the lake of Zurich, where they sometimes 

 occur in the spring and summer in quite enormous quantities, 

 while their number in winter is very much reduced. 



The permanent freshwater basins are of very different 

 characters. Thus, for example, the peat-mosses display an 

 abundant microscopic fauna. In Switzerland we find such 



* Abstract of an address delivered on November 22, 1886, before the 

 Naturforscbende Gesellscbaft in Zurich (' Zoologischer Anzeiger,' 3rd 

 and 17tb January 1887, pp. 13 and 33). 



