1916 Smith; on Salmon Development 97 



minute. Observation of those in the dark showed them to be lying on the 

 bottom of the flask ahnost without motion, and showing no symptoms of 

 being uncomfortable. Their respiratory movements were but 50 to the 

 minute. 



At 9:30 A. M. those in the light were decidedly more restless and 

 were frequently seeking air at the surface of the water. They still pos- 

 sessed perfect power of control and oriented themselves in a normal way. 

 No change was observable in those in the dark. 



At 10:30 A. jNI. observations were again made. Those in the light 

 showed a decided tendency to keep in the upper strata of the water while 

 those in the control remained in the lower. Those upon which the experi- 

 ment was being made were not orienting themselves in a normal wa3\ In- 

 stead of maintaining a horizontal position they floated with the longi- 

 tudinal axis of the body at a considerable angle to the horizon. At 10:45 

 their respiration movements were 67 per minute. Those in the dark 

 showed no signs of being uncomfortable at this time. 



At 12:55 P. M. those in the light were fast losing the power to di- 

 rect their movements normally. They darted about in an uncertain way 

 and as they settled on the bottom turned on their sides. In the dark flask 

 the fish were beginning to show signs of uneasiness and were seeking the 

 upper strata of the water, but there was no signs of exhaustion. 



At 2:25 P. M. those in the light were showing very marked signs of 

 exhaustion. Five were floating in the neck of the flask at the surface 

 of the water. The remaining ones were constantly darting to the upper 

 part of the flask and then settling downward tail first to the bottom 

 where they lay on their sides. Their respirations had increased to 94 

 per minute. Those in the dark showed little disposition to swim about 

 actively. They occasionally went to the surface. Their loss of power to 

 move in a normal way was not so marked as that of those in the light 

 two hours before. Their respiratory movements were 89 per minute. At 

 3 P. M. those in the dark exhibited about the same degree of exhaustion 

 shown by those in the light at 12:55 P. ^I. 



At 4 P. M. those in the light were lying in a helpless and dying con- 

 dition on the bottom, while those in the dark were in a condition similar 

 to that shown by the fish in the light at 2:25 P. M. There can be no 

 doubt but that the greater activity on the part of the fish in the light 

 resulted in a more rapid exhaustion of the oxygen contained in the water, 

 and a greater production of the waste products of metabolism which 

 would lead to the earlier exhaustion of the active fish. It would seem, 

 therefore, a fair conclusion to draw from this experiment that activity is 

 one of the most important factors in bringing about the difference in 

 weight between the two groups of fishes. 



