RHEOTACTIC REACTION OF STREAM ISOPODS. 65 



of secondary importance in their maintenance of position in 

 streams. 



3. The sign of the rheotactic reaction is of primary importance 

 in this regard in that an isopod oriented positively can withstand 

 approximately twice the current strength of one oriented in the 

 opposite direction. 



4. The clinging ability of positively oriented isopods varies 

 somewhat w r ith the degree of positiveness of the rheotactic 

 reaction which in turn is closely correlated with the metabolic 

 conditions of the isopods. 



5. The molting period and breeding season are especially 

 important in the ecology of stream isopods in that they directly 

 decrease the clinging ability and indirectly affect it by lowering 

 the tendency to give positive rheotactic reactions. 



6. Beyond possessing irritable protoplasm isopods are no more 

 adapted to the stream environment by reason of their positive 

 rheotaxis than the stream is adapted to the isopcd by virtue of 

 presenting the complex of environmental conditions best cal- 

 culated to call forth and maintain positive rheotaxis. 



LITERATURE CITED. 

 Alice, W. C. 



'n Seasonal Succession in Old Forest Ponds. Trans. 111. Acad. Sci., Vol. 4, 



pp. 126-131. 

 '12 An Experimental Analysis of the Relation Between Physiological States and 



Rheotaxis in Isopoda. Journ. Exp. Zool., Vol. 13, pp. 269-344. 

 '13 The Effect of Molting on Rheotaxis in Isopods. Science, N.S., Vol. 37, 



pp. 882-3. 

 '133 Further Studies on Physiological States and Rheotaxis in Isopoda. Journ. 



Exp. Zool., Vol. 15, pp. 257-295. 

 '14 Certain Relations between Rheotaxis in Isopods and their Survival Time in 



Potassium Cyanide. Journ. Exp. Zool., Vol. 16, pp. 397-412. 

 Alice, W. C. and Tashiro, Shiro. 



'14 Some Relations between Rheotaxis and the Rate of Carbon Dioxide Pro- 

 duction of Isopods. Journ. An. Beh., Vol. 4, pp. 202-214. 

 Mathews, A. P. 



'13 Adaptation from the Point of View of the Physiologist. Am. Nat., Vol. 47, 



pp. 90-105. 

 Henderson, L. J. 



'13 The Fitness of the Environment. An Inquiry into the Biological Fitness 



of the Environment. MacMillan, New York, 317 pp. 

 Shelford, V. E. 



'n Ecological Succession, I. Stream Fishes and the Method of Physiographic 



Analysis. BIOL. BULL., Vol. 21, pp. 9-36. 



