450 



HOVEY JORDAN 



The two records, while showing slight variations, are remarkably 

 alike in the time of response and the number of different positions as- 

 sumed in changing from an almost lateral orientation to an approxi- 

 mately posterior one. It should be noted that in this series of orien- 

 tations 75 per cent of the positions 

 were posterior, and that, as in figure 

 3, no anterior positions were as- 

 sumed. It seems, then, that the 

 eyes of the hamlet are not the es- 

 sential rheotropic end organs. 



In an effort to locate the cells 

 which are stimulated by the cur- 

 rent, the skin was stripped from 

 one of the more sensitive body 

 areas. It was impossible to obtain 

 any response from a current which 

 was directed against the subcuta- 

 neous structures (muscles, etc.) 

 thus exposed. In a few cases in- 

 definite reactions, which were much 



slower than normal, were observed, 

 but they were not characteristi- 

 cally rheotropic in nature. These 

 results lead one to the conclu- 

 sion that the end organs concerned 

 in rheotropism are located in the integument. 



Fig. 5. Twelve successive positions 

 assumed by a blinded fish in response 

 to the current C. As in figure 3, only 

 six positions are shown in each diagram. 



TABLE 3 



Time elapsed in assuming positions 1-12 (fig. 5) 



NUMBER OF THE POSITION 



The problem of determining the particular type of sense organ which 

 is sensitive to these currents is resolved, . then, into a physiological 



