66 THE AGE AND GKOWTH OF SALMON AND TEOUT. 



on August 19, it could not have been long since its winter-growth and the 

 formation of the winter-band was completed. 



Exactly similar conditions appeared in all the scales I examined, as 

 may be seen by referring to Table XXVIIc. If we examine the various 

 individuals in this table, we frequently notice that the increase of length 

 acquired by each fish since the last completed winter was very small 

 compared to the total increase between that and the previous winter. 



As an instance we will take No. 38, caught on July 30. Its course of 

 life has been as follows : 



Thus during its last summer the increase in growth only amounted to 

 1*5 cm., whereas between the formation of the seventh and eighth winter- 

 zones it had grown 9'5 cm. 



Exactly similar conditions appear in all the specimens, and we may 

 therefore conclude that summer-growth in Mjesen begins late. This is 

 very probably due to the somewhat remarkable conditions of temperature 

 prevailing in this lake. Its main source of supply, the Laagen, brings 

 down a great deal of icy water until late on in the summer, and it is 

 therefore late before the waters of Mj0sen begin to rise in temperature. 



The temperature records published by Herr Hvitfeldt-Kaas* show this 

 clearly. I give as an example the following from his series of records for 

 the year 1909 : 



Date and Temperature + C*. 



From these figures it is evident that the rise in temperature of the 

 upper surface of Mj0sen is late, and that by way of compensation it is also 

 late in cooling down. Thus the greatest warmth is in September, and even 



* " Temperaturmessungen in dem See Mj0sen," etc. Archiv f. Mathm og Naturv. 

 Vol. XXVH., n. 2, 1905. 



