286 KNUT DAHL. 



represent the fry of two different years or two annual classes 

 of growth, and the presence of the older one is dependant on 

 a biological peculiarity, distinguishing the trout from the salmon. 

 The young trout, indeed, after the lapse of the first summer in 

 the sea return to the river in autumn, spend the winter there 

 and again emigrate in spring. This phenomenon however, seems 

 mainly to apply to the larger rivers and streams. 



Thus if we examine the next two columns of tab. V which 

 are based chiefly on fishes caught in the mouth of the Børs- 

 elven in Gulosen and the „Skougdalselven" in Rissen, we find 

 only the smallest group of emigrants represented. The first of 

 these streams is hardly more then a brook, and it is perfectly 

 clear, that numbers of larger fishes cannot spend the winter 

 there. Neither is the second stream an important watercourse. 



As an example I propose to describe my results from one 

 river, the Orkla, which at all times of the year has been exa- 

 mined by me. 



If the first column of table V be compared with table VI 

 it will be observed that the smallest group, which in May 1898 

 was 10 — 20 cm. long, in October of the same year had grown 

 to a size varying between 18 and 30 cm. and at this latter time 

 of the year occurred in large masses in the mouth of the Orkla. 



All the fishes (between one and two hundred) by means of 

 which the first column of table VI is constructed, were taken 

 in 3 hauls with the eelhandseine and it was evident, that the 

 trout were „thick as herrings" in the lower course of the river. 

 As will be seen in the table, only an insignificant minority of 

 these fish were sexually mature, and consequently their object 

 was not propagation. 



On this same occasion also a stretch of the river at Forve, 

 7 kms. up the river, was examined. Not a fish was caught. 

 At Kalstad in the Meldal about 40 km. up the river, a number 

 of hauls were effected in a larger stretch of the river. In these 

 hauls I obtained the fishes denoted in the next column of table 



