440 HOVEY JORDAN 



their heads directed away from the hose pipe, most of the time with 

 the body axis in line with the current, so that a group of fishes showed 

 a fanlike arrangement corresponding to the spreading currents of water 

 C, as shown by the arrows in figure 1. 



In order to determine the exact nature of this reaction, experiments 

 were undertaken both on groups of fishes and on individuals. The 

 study of groups showed that this peculiar orientation was not altogether 

 constant, but that some of the fishes assumed from time to time posi- 

 tions more or less oblique to the current. The precise significance of 

 this was manifest only when the actions of individual fishes were ob- 

 served continuously. 



In an effort to ascertain the precise mechanism by which these reac- 

 tions were brought about, and if possible to determine the nature of the 

 stimulus inducing them, a small but strong localized current of water 

 was directed in succession against different areas of the body. This re- 

 vealed varying sensitivity on different areas; furthermore the effect of 

 a narcotic on these areas indicated both the position and the probable 

 nature of the end organs involved in these responses. 



B. Review of literature 



Up to about fifteen years ago it was generally held that the orien- 

 tation and locomotion of organisms in a current of water where- 

 by the anterior end is directed against the current and a swimming 

 motion causes either an advance or the maintenance of a comparatively 

 stationary position against the flow was due to the direct mechanical 

 action of the current and was in the nature of a reaction to pressure. 

 Stahl in 1884 described such a phenomenon in Myxomycetes and Ver- 

 worn (1) in his Allgemeine Physiologic (p. 428) interprets it as a positive 

 response to pressure stimulation. Lyon (2) (p. 157) says that reac- 

 tions of blinded fishes [Fundulus?] to currents flowing through troughs 

 may perhaps be caused "by higher pressure on one part than on the 

 other, through differences in the velocity of the water striking the two 

 parts." He here introduces the theory of unequal pressures on various 

 parts of the fish's body in contrast with "the gross mechanical one of 

 Radl." 



The one early exception to the theory of pressure stimulation by cur- 

 rents seems to have been the idea advocated by Schulze (3), that the 

 lateral-line organs were stimulated by the movement of water against 

 them. This view has, however, been adequately disproved by Parker 

 (4). 



