Reighard. — Senses and Learning in Fishes 143 



organs was long a matter of controversy — but through 

 the work of Professor Parker and others it is now known. 

 From numerous experiments chiefly on the salt-water 

 killifish (Fundulus heteroclitus) , Parker (1903, 1903a, 

 1905, 1910b), concluded that the lateral line organs are 

 not affected by light, heat, degree of saltness of the wa- 

 ter, food, oxygen, carbon dioxide, foulness of water, wa- 

 ter pressure due to the varying depth at which the fish 

 may be, water currents or sound. Parker's method was 

 to cut the nerves to the lateral lines in a number of indi- 

 viduals and to compare the behavior of these individuals 

 with that of normal fish when the two were subjected to 

 the various stimuli listed above. In the operated fish 

 the lateral line organs were not in use while in the nor- 

 mal fish they were functioning in the usual way. If the 

 two sets of fish behaved in the same way when subjected 

 to these various stimuli it was concluded that the stimuli 

 did not affect the lateral line organs. If the normal fish 

 were affected by certain stimuli to which the operated 

 fish did not respond it was concluded that this failure 

 to respond was due to the fact that the lateral line or- 

 gans were not functioning in the operated fish. In the 

 case of current for example it was found that all normal 

 and operated killifish tested swam against the current 

 and that it was impossible to detect any difference in 

 their behavior toward it. The conclusion was that cur- 

 rent did not affect the lateral line organs. By this meth- 

 od Parker found but one stimulus that affected the lateral 

 line organs of the killifish. When normal killifish were 

 placed in an aquarium they came, after a little time, to 

 swim near the surface. If then the table on which the 

 aquarium rested was gently rocked by a person invisible 

 to the fish, they darted at once to the bottom. Fish in 

 which the lateral line nerves had been cut did not show 

 this behavior, but remained near the surface of the wa- 

 ter. The operated fish were in no way affected by the 

 movement imparted to the water unless they came so 

 near the top of the aquarium as to feel the ripples on the 

 surface of the water. They then descended a little until 



