BEHAVIOR AGREEMENT AMONG ANIMALS. 305 



1 1/2, 2, 2. l /2 had been beaten to give a surface like stone. These 

 two pans were placed side by side beneath the lamps which were 

 25 cm. apart and 28 cm. above the bottom. Water flowed 

 around the pans and kept them at a temp, of 14 C. Water 

 in the pans I to 2 cm. deep. 



2. SPECIFIC PECULIARITIES. 

 Rapids Community. 



Etheostoma and Cambarus readings every 30 sec. begun at once. 



Goniobasis: 40 watt tungsten lamps were substituted to in- 

 crease activity and the experiment was read every half hour 

 (due to inactivity). The animals were placed in a row on the 

 boundary between sand and hard material, in some cases so that 

 they would extend and come in contact with the sand in others, 

 with the hard material. When they became active, they crept 

 from the sand to the hard bottom in all cases and usually turned 

 back when moving from the hard bottom to sand. The reaction 

 to sand and hard bottom in this species was influenced by 

 reactions to gravity because while the sand and hard bottom in 

 the experiment were at the same level the foot settled into the 

 sand enough to make the hard bottom higher and the mollusks 

 tend to crawl upward. The results are legitimate because in 

 their natural habitat the animals can avoid sand by this means. 



Hydropsyche. Readings every minute, begun after 3 min. 

 They often turned back on reaching the sand and were more 

 active while on it. 



Argia. Readings every minute, begun after three minutes. 



Perla. Readings every minute, begun after one minute. 



Heptageninae. Readings every minute, begun after one min. 

 Turn back on reaching the sand. 



Psephenus. Readings every minute, begun after five minutes. 

 The animals are evidently much irritated by the sand as they 

 wave the thin margins of their bodies about, walk high on their 

 legs and when once in contact with the hard bottom they come 

 to rest and cling for days if not loosened. 



Pool Community. 



Notropis, Hybopsis, and Ambloplites apparent!}' do not react 

 to bottom when in small experimental boxes. 



