54 A. J. Silfvenius, Ein Fall von Schädlichkeit der Trichopterenlarveu 



long (the length that has been stated in Sweden) are about 

 1 V'i years old — a sufficient time for their Coming up there 

 from the southern Baltic, Kattegat or Skagerack. 



About the migration of the adult eel along our coasts we 

 know at present verv little. In the year 1899 The Fisheries 

 Society of Finland arranged the first experiments with eeltraps. 

 For that purpose an experienced eelfisher from southern Sweden 

 was engaged for nearly two months. Following the Instructions 

 given by him, Mr Hugo Sauren has on his estate Hirsala, in 

 the parish Kyrkslätt, some miles westward from Helsingfors, 

 succeeded in getting considerable numbers of eel. In the summer 

 1901 he caught 857 eels, the most part weighing between V/., 

 and 1 kg. About 400 of these eels he got in August. The 

 experiments of Mr Sauren show that on the south-coast of Fin- 

 land the grown up eels are wandering we s t ward. Some exper- 

 iments with eeltraps made by the said Swedish fisherman, a 

 Danish fisher and by myself have not yet given any posi- 

 tive results. The chief difficulty for us is, that the coast is 

 mostly broken up in a väst archipelago, wher3 it is difficult to 

 find the principal ways of the eel. 



Ein Fall von Schädlichkeit der Trichopterenlarven. 



Von 

 A. J. Silfvenius. 



Im Herbst 1901 wurden von Herrn Ingenieur L. Sallmén 

 einige Blöcke, die dem Unterbau einer Brücke, welche über den 

 Jyränkö-Wasserfall in der Nähe von Heinola führte, entnommen 

 waren und auf der ganzen Oberfläche unregelmässige klei- 

 nere und grössere Vertiefungen zeigten, zu näherer Unter- 

 suchung nach Helsingfors gesandt. Exemplare von Insekten- 

 larven, die in ungeheurer Menge auf diesen Blöcken gefunden 

 worden waren und vermutlich die Vertiefungen ausgenagt hatten, 



