1916 



Smith; on Salmon Development 



93 



9.85 per cent more than those developed in the light. The next 

 day, January 9, 12 fish were picked at random from each trough and ac- 

 curate measurements were taken as follows : length from tip of snout to 

 base of middle ray of caudal fin, greatest depth, greatest thickness, length 

 and width of ventral yolk-sac opening. 



The length of those living in the light varied between 30 and 33.5 

 mm. with an average of 31.1. The greatest depth, which was through the 

 center of the yolk-sac, varied between 6.3 and 7.7 mm. with an average 

 of 7.1 ; the greatest thickness varied between 4.7 and 5.6 mm. with an 

 average of 5 ; the ventral opening of the yolk-sac varied in length between 

 8 and 10 mm. with an average of 9.2, and the greatest width of this open- 

 ing varied between 1.2 and 4.2 mm. and averaged 2.6. 



The length of those taken from the dark varied between 29 and 

 S3 mm. with an average of 31.5; the depth varied between 7.2 and 8.5 mm. 

 with an average of 7.9; the thickness varied between 5 and 6 mm. with an 

 average of 5.4; the length of the ventral yolk-sac slit varied between 9 

 and 10.7 mm. with an average of 9.9; and the greatest width of the slit 

 varied between 2.4 and 5.5 mm. with an average of 4.1. 



These figures show an average difference in size in favor of those 

 kept in the dark of .4 mm. in length, .8 mm. in greatest depth and .4 mm. 

 in greatest width. The yolk-sac opening averaged .7 mm. longer and 1.5 

 mm. wider in those from the dark than in those from the light. The 

 diflference in breadth and thickness between those in the dark and those 

 in the light indicated that there was a considerably greater absorption of 

 yolk material by those in the light. 



In order to determine this difference accurately 12 fisli were taken 

 at random from each trough on January 1 8 and placed in a five per cent 

 solution of formalin for seven days. At the end of this time the yolks 

 were so hardened that they could be easily separated in mass from the 

 fish. The fish were dried first on a linen towel and then carefully on 

 filter paper. The 12 from the dark trough weighed 6.240 grams and the 

 12 from the light trough 5.820 grams. The yolk-sacs were then carefully 

 dissected out and those of the 12 fish from the dark trough weighed .930 

 grams, while those of the 12 from the light weighed .790. From these 



