452 HOVEY JORDAN 



This fact indicates that those sensory cells which are stimulated by 

 touch and defunctionized by cocaine are also the cells which are the 

 primary end-organs of the rheotropic response. 



3. Summary of end-organ determination. 1. The end organs of the 

 hamlet essentially concerned in rheotropism are located within the 

 integument. 



2. The regional distribution of sensitivity to a water-current and to 

 touch is the same. 



3. Cocaine applied to the lips for about three minutes renders those 

 organs insensitive both to touch and to currents. 



4. These facts indicate that the end organs of touch serve also as 

 the essential end organs of current stimulation in the hamlet. 



5. Other sensory cells may be more or less affected by currents in 

 some fishes, but they appear to be only accessory end-organs of rheo- 

 tropism, and in the responses described in this paper they evidently 

 play no part at all. 



III. DISCUSSION 



There is much evidence to show that the rheotropic responses of the 

 hamlet, as suggested for Fundulus by Parker (4) (6), are effected chiefly 

 by the tactile corpuscles. His attempt to prove this by immersing the 

 entire fish in a solution of cocaine did not succeed because the general 

 action of the drug entirely destroyed all sensitivity and movements of 

 the fish; but the great sensitivity of the lips of the hamlet has afforded 

 an excellent opportunity to study changes in the fish's behavior result- 

 ing from the local application of this narcotic. In this case regional 

 anaesthesia, producing insensitivity to touch, is as satisfactory as gen- 

 eral narcotization would be, because it causes a most unique rheotropic 

 response totally to disappear. 



Some of Lyon's experiments (2) on rheotropism, from which he con- 

 cluded that the reaction of Fundulus to currents is chiefly to compen- 

 sate the transporting effect of the current, seem to furnish evidence 

 that the integumentary cells (tactile corpuscles) were directly concerned 

 in the rheotropism which he observed. Among these is experiment 9 

 (p. 157), in which a blinded fish, without touching any solid object- 

 often required for orientation by fishes without eyes headed into the 

 rushing current. This certainly may be interpreted as a response to 

 direct tactile stimulation of the integument by the water, and Lyon 

 himself admits that this may be called a true rheotropism. In his 

 opinion, however, it is due to the "sliding contact" (stereotropism) 



