EXPERIMENTAL WORK. 201 



water which had passed through the 20-feets along the other side 

 of the 60-feet, and this water was afterwards collected and re- 

 distributed to the next series of ponds (the 130-feets). 



This finishes the work of construction belonging to season 

 1875-76, the 60-feet pond being filled for the first' time on 24th 

 June 1876. 



SEASON 1875-76. EXPERIMENTAL WORK. 



The experimental work of this season was chiefly with a view 

 to ascertain the percentage of incubation accomplished in each 

 period of twenty-four hours by an ovum in water of varying 

 temperature. I calculated by a table based on Stone's dictum that 

 at 40 F. a trout egg takes 100 days to hatch. Subsequent 

 experience has shown that there is a slight difference in the time 

 occupied in hatching by the eggs of various species of Salmonidce ; 

 and that hybridism, the age of the parents especially the age of 

 the male, causes a prolongation of the period, or the reverse. 

 Happily for the results, only two classes of eggs were dealt with, 

 viz. S. levenensis and S. fario. The former were all spawned at 

 the lake from obviously mature parents, and the results from these 

 eggs may be depended upon. The S. fario eggs were obtained 

 from small hill -burn trout, and these probably varied much in 

 age. They were, however, all apparently sexually mature. 



I kept a careful record of the temperatures of the air and 

 water ; and from the corrected average temperature of the latter 

 the percentage of incubation of the twenty-four hours was calcu- 

 lated. Unfortunately, I have not kept the original readings in 

 decimals of a degree, which were marked in my rough note-book. 

 In the clean note-book I have only entered the nearest degree, so 

 it is impossible to check the calculations ; they were made and 

 entered from day to day, and I believe them to be accurate. 

 They were originally worked to four places of decimals, although 

 only two places were entered in the clean copy. The importance 

 of this table lies in the wide range of temperature that occurred in 

 the winter 1875-76 at Middle third, in which hatching-house the 

 record was taken. The ova was laid down on twelve different days. 



