82 



WALTER E. CARREY. 



A study of the orientation of any individual fish gives the 

 following result : When a fish is headed exactly toward the 

 moving object a movement in any direction may be elicited, up, 

 down, or to either side, by simply moving the object in a direction 

 opposite to that which it is desired to make the fish take, as is 

 indicated in Fig. 7, a. If the fish's long axis forms an angle with 

 the line of motion of the stimulating object, the direction of turn- 

 ing in assuming its reflex orientation will depend upon which way 

 the animal is heading. If it has somewhat the " and "-postion 

 with reference to the motion (Fig. 7, b) it will turn further into 

 that position until its axis is parallel to the line of motion, but if 

 it has the " homo "-position (Fig. 7, c] the reaction is not so 

 certain. The fish will of course be oriented as we have already 

 described, but it usually backs off in a hesitating way and may 

 then turn in either direction as is indicated by the two arrows, 

 usually however it turns in the longer arc of a circle as is indi- 



A 



FIG. 6. 



cated by the arrow at x, at least this is usually the case when 

 the stimulating object is moved quickly. With a slower motion 

 the fish usually moves through the shorter arc just as is indicated 

 in a and b, Fig. 7. 



The reactions of a number of kinds of small fish were tested 

 among them Fnndnlns nmi-galis, Fitndiilus Jictcroclitus, small eels 

 and young sea robins, but without eliciting the reflex. Young 

 mackerel however behaved in a manner very similar to stickle- 

 backs, but the reactions were not so precise. 1 



1 This reflex of sticklebacks is not invariably nor even easily obtained in small 

 aquaria ; the aquaria of the P'ish Commission are about six feet long. Dr. Gaylord 

 Clark informs me that he has tested sticklebacks for this reaction in the open water 

 off the wharves, with positive results. 



