THE BEHAVIOR OF BROOK TROUT EMBRYOS 51 



tively to current. But they were usually unable to swim more 

 than a few centimeters, or able merely to orient themselves, 

 owing to the size of the yolk sac. 



While none of the Brook Trout were persistently negative 

 in their reactions to current, there were always a few which did 

 not give a definite positive response. Since it was noted that 

 a fish was sometimes carried backward farther than it was able 

 to advance, the four embryos in experiment number two which 

 did not react definitely- were tested later in the light, where 

 they could be watched. One fish did not swim at all. Three 

 fish were carried backward, but oriented toward the source of 

 the current. They struggled to advance, but were unable to 

 do so. Therefore, these were actually positive. 



Of the twenty-one which are marked positive, five were evi- 

 dently weak; their condition somewhat resembling the three 

 just mentioned. Since these were found on being tested in the 

 light to be clearly positive, and on the third trial in the dark 

 progressed decidedly toward the current, they were included 

 with the trout which had just been observed to move definitely 

 against the current. 



In order to discover whether surrounding objects affect the 

 reaction to current, a striped paper was passed back and forth, 

 beneath and at the sides of the glass dish containing Brook 

 Trout about three weeks old. No reaction resulted. Brook 

 Trout were also placed in a round glass dish set within another 

 dish and a current of water made to run between the dishes. 

 To this also the fish failed to react. Hence during the first 

 few months, the sense of sight appears to have little or no rela- 

 tion to the reaction of Brook Trout to current. This does not 

 agree with what Lyon ('04) believed to be true regarding the 

 fishes with which he worked. 



Positive rheotropism was also exhibited by a school of German 

 Brown Trout two or three months old, that were almost invari- 

 ably found resting or swimming about near the source of the 

 current in the trough where they were kept. On testing Rain- 

 bow Trout three days old, when the yolk sac is enormously 

 large, forty or fifty per cent were observed to be positive to 

 current, while sixty per cent were indifferent, the latter either 

 lying quiet or whirling about without orienting themselves when 

 stimulated. 



