158 ZOOLOGY: H. JORDAN 



period the time occupied from the beginning of one set of 'swinging 

 motions' to the beginning of the next; thus the posterior orientation, 

 which is of longest duration, is the last phase of the orienting process. 

 A characteristic reaction, then, of Epinephelus striatus is posterior or 

 lateral orientation to a current. Since in a majority of cases the orien- 

 tation is posterior, and since this is maintained longer than any other 

 position, it is a fair inference that this is the significant reaction. 



Various regions of the body were explored with a localized current 

 (1/28 liter per second) directed through a long glass tube, the experi- 

 menter being invisible to the fish. The following areas were found to 

 be sensitive, but the response varied in promptness. Stimulation of 

 the lips (if prolonged it causes a relatively violent reaction) brought 

 forth a response in 7 seconds; the caudal fin in 16 seconds; the dorsal 

 fin in 22, the cheek and operculum in 25, and the side of the body in 30 

 seconds. From these observations it is clear that the lip region is much 

 the most sensitive part of the surface of the body, and the possibility 

 is at once suggested that the posterior orientation of the fish is a reac- 

 tion which serves to protect this region from the action of the current. 

 This seems the more probable from the fact that prolonged stimulation 

 of this region by the current employed in the experiment always caused 

 a rather extraordinary and violent reaction. 



Several end organs have, at one time or another, been regarded as 

 the receptors in the case of rheo tropic responses: lateral-line organs 5 

 (Schulze, '70); the organs concerned in response to pressure 7 (Ver- 

 worn, '97, p. 445ff., barotaxis), and the ear 6 (Tullberg, '03). 



Two other views have been advocated, first, that it is the tactile cor- 

 puscles which are stimulated by currents 3 - 4 (Parker, '03a, '03b) ; second- 

 ly, that it is chiefly the eyes which are stimulated, this being due to the 

 transportation of the fish through the water. According to this view 2 

 (Lyon, '04), rheotropic reactions are chiefly optic reflexes, which serve 

 to compensate the apparent motion of the visual field. This is an in- 

 direct effect, a direct stimulation being produced only when the fish 

 is in contact with some part of the solid environment. This, in the case 

 of blind fishes, Lyon thinks acquaints the animal with its transporta- 

 tion and a compensatory swimming results. 



In studying the question of rheotropic end organs, observations to 

 be described elsewhere were made which confirm the idea that sense 

 cells of pressure and equilibration are unaffected by water currents. 

 The lateral-line organs and the eyes, which can be rendered function- 

 less by appropriate operations, are also unaffected. The skin was 

 next removed from certain body areas and the underlying tissue was 



