442 HOVEY JORDAN 



compensating motions; "the current playing only the passive part of 

 sweeping the fish against objects on the bottom." 



In view of Lyon's observations and general conclusion that the 

 current itself does not stimulate the skin of Fundulus directly, except 

 as it acts like a solid object of considerable size, it seems desirable 

 to determine whether, in other fishes, the integument is sensitive to 

 water-currents, and also whether the eyes have any essential part in 

 the rheotropic reactions. 



II. DESCRIPTION OF EXPERIMENTS 



A. Posterior- and lateral orientation 



1 . In groups of fishes. The positions assumed by a group of fishes 

 under the conditions already described gave, in general, the fanlike 

 appearance shown in figure 1 ; but it was also to be seen that, from time 

 to time, one or more individuals assumed a different position, the body 

 swinging around so that its long axis was almost or quite perpendicular 

 to the current; and sometimes, though rarely, an individual would be 

 headed more or less directly into the current in the manner of the hith- 

 erto described reactions of fishes generally. In order to test roughly 

 the quantitative relations at any given instant between these various 

 positions, several series of observations were made, both during the day 

 and at night, on a group of seven fishes which had become habituated 

 to their surroundings. One such series is recorded in table 1; all the 

 others are nearly identical with it. 



From table 1 it will be seen (1) that, although the majority of 

 fishes (67.1 per cent) tailed into the current, many individuals (31.9 

 per cent) so placed themselves that the current hit the side of the 

 body; and (2) that less than 1 per cent headed into the current. These 

 records were taken at about two-minute intervals. While they show 

 that the hamlet in its normal responses to a current may assume one 

 or the other of two positions, they do not afford sufficient evidence of 



2 In describing the various positions of orientation which a fish may assume, 

 I shall use posterior orientation to denote positions in which the tail is directed 

 toward the oncoming current or to points not more than 45 degrees from it on 

 either side; lateral orientation to denote positions in which the long axis of the 

 body is perpendicular to the direction of the current or makes an angle with the 

 perpendicular on either side not greater than 45 degrees; and anterior orienta- 

 tion to positions whereby the head is directed straight into the current or to points 

 not more than 45 degrees from it on either side. 



