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THE AMERICAN NATURALIST [Vol.LVI 



labeled at the proper points so that from a single ob- 

 servation post, record could be taken of the distances 

 traveled by fishes responding to the streams flowing down 

 the incline. 



Streams were introduced after temporary storage in 

 two barrels located above the ends of the experimental 

 troughs. In some experiments the inflowing currents 

 came directly from the circulation pipes of the laboratory. 



Experiments were performed with sea wat^r, fresh 

 water and combinations of the two, followed by tests with 

 the individual salts of sea water in w/10 solutions. Tem- 

 perature and stream flow were varied and proved most 

 important adjuncts to the salts in affecting behavior. 



In order to be quite certain that habit formation as a 

 factor was eliminated, it was customary to select a trough 

 used during the night for sea water inflow and introduce 

 a substance less attractive, for the first few experiments 

 with a group. As conditions of illumination were uni- 

 form and the troughs were so near each other, this proce- 

 dure probably reduced the error due to a habit factor. 



The fish were males, selected for apparent vigor and 

 averaged about 12 centimeters in length. They were used 

 for a complete series of experiments in lots of ten, then 

 replaced by another ten of similar size. In the majority 

 of the exi)eriments, the species used was Fundulus hete- 

 roclitus. Its habits throughout the year were already 

 known to the writer (1916, 1920). Loeb, Thomas and 

 others .had already studied its susceptibility to toxic sub- 

 stances. It is anadromous, highly resistant, yet furnishes 

 quick reactions. 



Fundulus majalis was used less frequently as it is not 

 so resistant to laboratory- conditions and behaves differ- 

 ently with reference to tides. The observations of Mast 

 (1915) made it especially desirable to study the reactions 

 to currents and accordingly a series of experiments was 

 made. 



Clupea harengus dies quickly in captivity. Its re- 

 sponses are extremely delicate and it has been used quite 



