298 VICTOR E. SHELFORD. 



confined the animals in the central portion of the apparatus. 

 Thirty-three centimeters above the bottom of the trough and 

 12-15 cm. from the respective ends were two 4-c.-p. carbon 

 filament lamps. The control box was placed alongside the current 

 trough and kept cool by streams of water. 



Water flowed into the left-hand well from the supply pipe. 

 The rates of flow were determined by measuring the amount of 

 water that flowed through the trough in cubic centimeters per 

 second. This was divided by the average area of the cross 

 section of the water flowing through the trough, which gives 

 the velocity in cm. per second (Finley's method). The velocity 

 is determined by (a) the volume flowing into upper well per unit 

 of time, (b) depth of water in trough, and (c] angle of slope. 



VELOCITIES USED AND FACTORS CONTROLLING THEM. 



Degrees Devia- Velocity in 



Volume per sec. Depth in Cm. tion from Level Cm. per Second 



200-250 c.c 4.0-5.0 o 4-6 



500-600 c.c 4.5-5.0 I 10-12 



500-600 c.c 2.5-3.5 2.5 16-20 



With very few exceptions five individuals were used. In 

 each case the animals were poured into the center of the trough 

 and readings begun after the animals had adjusted themselves to 

 the current. This time differed greatly with different species, 

 to a less extent with different lots of the same species. The 

 differences between different species are due largely to different 

 speeds of movement. Variations of the second kind were in 

 strong current and due to the particular way in which the animals 

 floated against the lower screen. The length of time before 

 the first reading is given in general terms for each species. 



2. SPECIFIC PECULIARITIES OF BEHAVIOR IN WATER CURRENT. 



(Time before first reading given in brackets.) 



Rapids Community. 



Etlieostoma (Fig. i) [15-30 sec.]. Rest on bottom head up 

 stream, move by darts, positively thigmotactic, often rest against 

 lower screen and often forced against it in very strong current. 



Cambarus (Fig. 2) [15-^0 sec.]. Creep on bottom. 



Goniobasis (Fig. 3) [30-40 min.]. Amount of activity is largely 



