520 S. O. MAST 



9. Reduction in the concentration of hydroxyl ions, increase in 

 anesthetics, increase in temperature, and decrease in hght, all 

 produce the same reversion in the sense of orientation, and this 

 reversion may also occur without any change in the environment. 

 It is, therefore, probably due to some specific change in the phys- 

 iological process in the organism, which may be induced by a 

 number of different factors. 



10. Reversion depends upon the time-rate of change in the 

 concentration or intensity of the effective factors in the environ- 

 ment, but it has not been demonstrated that it depends upon the 

 time-rate of change in the physiological processes which are 

 involved in reversion. 



LITERATURE CITED^ 



Allee, W. C. 1918 Reversal of phototaxis and carbon dioxide production in 



May-fly nymphs. Anat. Rec, vol. 14, pp. 95-96. 

 Arisz, W. H. 1915 Untersuchungen iiber den Phototropismus. Ex. d. Rec. d. 



Trav. hot. Neer., vol. 12, pp. 44-213. 

 EsTERLY, C. O. 1917 Specificity in behavior and the relation between habits 



in nature and reactions in the laboratory. Univ. of Cal. Pub. in Zool., 



vol. 16, pp. 381-392. 

 EwALD, W. F. 1914 Versuche zur Analyse der Licht und Farbenreaktionen 



eines Wirbellosen (Daphnia pulex). Zeitsch. f. Sinnesphysiol., Bd. 



48, S. 285-324. 

 Gamble, F. W., and Keeble, F. 1903 The bionomics of Convoluta roscofTensis, 



with special reference to its green cells. Quar. Jour. Micr. Sci., vol. 



47, pp. 363-431. 

 Holmes, S. J. 1901 Phototaxis in Amphipoda. Am. .Jour. Phys., vol. 5, pp. 



211-234. 



1905 The reactions of Ranatra to light. .Jour. Comp. Neur. and 

 Psyc, vol. 15, pp. 305-349. 



1906 Studies in animal behavior. Boston, 266 pp. 



Loeb, J. 1905 Studies in general physiology. Chicago, vol. 1, 423 pp. 



Mast, S. O. 1907 Light reactions in lower organisms, II. Volvox. Jour. Comp. 



Neur. and Psyc, vol. 17, pp. 99-180. 



1911 Light and the behavior of organisms. New York, 410 pp. 

 OsTWALD, W. 1907 Zur Theorie derRichtungsbewegungniedererschwimmender 



Organismen, III. Arch f. d. ges. Phys., Bd. 117, S. 384-408. 

 Washburn, Margaret F. 1917 The animal mind. Second edition. New York, 



386 pp. 



^ For a fairly complete list of references to the literature on reversal in the 

 sense of orientation, see Washburn ('17, pp. 200-214), Holmes ('16, pp. 116-119), 

 and Mast ('11, pp. 264r-287). 



