426 W. C. ALLEE AND E. R, STEIN, JR. 



selves in the swift current. In April and Alay large numbers of 

 Leptophlebia were found among submerged leaves in the quieter 

 parts of the brook. At the same time Epeorus was most abun- 

 dant under stones in more rapidly moving water. Neither were 

 found on the upper surface of stones until late in May when the 

 adults were emerging in large numbers. At this time hundreds 

 of Epeorus nymphs could be seen on the upper side of any large 

 stone in the brook, all headed against the current. 



METHODS 



The phototactic tests were made in a large, light-tight wooden 

 box to which light was admitted through adjustable slits. The 

 opening was near the bottom of the box so that the light entered 

 the end of the experimental dishes. During the experiments 

 described in the first part of this report a north window fur- 

 nished the light source. The experimental box was painted dead 

 black inside. The rear was curtained with a heavy black, cloth. 

 A semicircular opening in the floor of the box opposite the light 

 inlet permitted the observer to sit with head and upper body in- 

 side the box without introducing an appreciable amount of light. 



The light-reaction tests were carried on in oblong glass dishes 

 measuring 12 x 5.2 x 2.2 cm., which were placed with the long 

 axes parallel with the light rays. When it was necessary to cool 

 the dishes to keep the temperature at or below tap temperature, 

 the experimental dishes were placed in shallow glass trays and 

 packed in ice on all sides except that toward the window. Control 

 dishes were kept under identical conditions save for the factor 

 under experimentation. 



The nymphs were kept in the laboratory in aluminum tea balls 

 which hung in running tap water which was similar in salt and 

 gas content to the water of their native streams. ^lost of the 

 experiments were performed before the animals had been in the 

 laboratory five days. 



