304 



VICTOR E. SHELFORD. 



remains large but the wide rock bass was forced against the 

 lower screen. Campdoma was less active. Macromia and Ca- 

 lopteryx were washed against the screen. Anodontoides and Sphce- 

 rium showed activity as usual. 



In the 16-20 cm. per sec. current only Notropis held out against 

 the current for the five minutes during which the readings were 

 taken. The other fish were swept against the screen very soon 

 as were the other animals except Anodontoides which was in- 

 active. Thus judging from (a) the amount of activity, (b) the 

 efficiency and (c) the number of positive orientations, the 4-6 cm. 

 per sec. current is probably nearest the optimum for the pool 

 community. 



IV. REACTIONS TO BOTTOM. 



i. METHOD. 



The tests were made in a dead black dark room under a hood 

 of black sateen which permitted observation from between the 

 symmetrically placed 4-c.-p. lamps clamped in a narrow slit 

 (Fig. 30). The experimental boxes were two bread pans 10x31x50 



FIG. 30. Showing the water tray and hood in which the pans were placed in 

 the study of reactions to bottom. The observations were made through the slit 

 between the lights. 



cm. The bottom of one was entirely covered with beeswax, 

 one half of the other with sand and the other half with 

 wax into which the Warsaw Co.'s quartz dust numbers 



I, 



