BEHAVIOR AGREEMENT AMONG ANIMALS. 



301 



in the direction headed, the diagrams are of perfect chance 

 inclefiniteness, counting an arc of thirty two degrees of the 

 possible circle of orientation as covering respectively positive 

 and negative trials. 



Comparing first the reactions of the rapids animals to the 

 different velocities, we note that the positive orientations in the 



STRAIGHT CURRENT 



4-6 CM. PER SEC 



HYDROPSYCHE OR RAPIDS COMMUNITY 

 PER CENT 10 30 30, 40 50 60 70 80 90 100 

 ETHEOSTOMA 



CAMBARUS 



GONIOBASIS 



HYDROPSYCHE 



ARGIA 



PERLA 



HEPTAGENINAE 



PSEPHENUS 



PER CENT 10 20 30 40 50 66 70 80 90 100 

 ETHEOSTOMA 



CAMBARUS 



GONIOBASIS 



HYDROPSYCHE. 



ARGIA 



PERLA 



HEPTAGENINAE 



PSEPHENUS 



ORIENTATION 



SAND-GRAVEL BOTTOM OR POOL COMMUNITY 

 Q 10 20 30 40 50 60 70 80 90 100 



NOTROPIS 



HYBOPSIS 



AMBLOPLITES 



CALOPTERYX 



CAMPFLOMA 



MACROMIA 



ANOOONTOIDES 



SPHAERIUM 



10 20 30 40 50 60 70 80 90 1QQ 



NOTROPIS 

 HYBOPSIS 

 AMBLOPLITES 

 CALOPTERYX 

 CAMPELOMA 

 MACROMIA 

 ANODONTOIDES 

 ' SPHAERIUM 



NO ACTIVITY I | 



FIGS. 1 8-2 1. Showing reactions to 4-6 cm. per sec, current in per cent, positive, 

 negative, indifferent, and inactive (18-19) and in per cent, active individuals posi- 

 tive, negative, and indifferent (20-21). The rapids community (18) shows a 

 large percentage of inactivity while the percentage of active positive (20) averages 

 less than 50. The animals of the pool community were nearly all active. The 

 first four non-burrowing species are strongly positive. It thus appears that 4-6 

 cm. per sec. is near the optimum for pool species. Temperature of water in experi- 

 ments: Rapids animals 16 C.; pool animals 9 C. 



4-6 cm. per sec. current are only a little greater than the negative 

 and indifferent, excepting Argia which is thrown into line by the 

 action of the current on the gill plates. The amount of activity 

 was different for the different species. 



