500 JOHN LINCK ULRICH 



indicates a high degree of the development of the reflex mechan- 

 isms in these rats. From these results it appears that the usual 

 distinction between a "habit" and an " instinct" is an artificial 

 one. The only distinction noted between a movement, as the 

 extensor thrust to plunge the plane, and a similar movement of 

 the extensor thrust to push light objects about, is that in the 

 first case an exaggerated performance of this thrust of the fore 

 limbs is used. In each case progression is inherently conjoined 

 with the extensor thrust, and for plunging of the plane an exag- 

 gerated performance of both movements is demanded. In a 

 great many rats this exaggerated performance of these move- 

 ments can not be produced, and for them the limitations to 

 effective adjustment to the environment of the problem are 

 observed to be present. 



(To be continued) 



REFERENCES 



(1) CARR, H.: Principles of selection in animal learning. Psych. Rev xxi 



1914. 



(2) WATSON, J. B.: Behavior, An Introd. to Comp. Psych., 1914. 



(3) HOLMES, S. J. : Studies in Animal Behavior, 1916. 



(4) LOEB, J. : Forced Movements, Tropism, and Animal Conduct, 191S. 



(5) CARLSON, A. J. : The Control of Hunger in Health and Disease, 1916. 



(6) CARLSON, A. J. : Amer. Jr. Physiol., xxi, 1913. 



(7) ELLIOTT, T.: Br. Jr. Physiol., xliv, 1912. 



(8) CANNON, W. B. : Bodily Changes in Pain, Hunger, Fear, and Rage, 1920. 



(9) CARLSON, A. J.: Ibid., 1916. 



(10) MAGNUS AND DE KLEIJN: Pfluger's Arch., 145, S. 455, 1912. 



(11) MAGNUS AND DE KLEIJN: Pfluger's Arch., 145, S. 178, 1913; 159, S. 163, 1913. 



(12) SHERRINGTON, C. S. : Brain, xxxviii, 1915. 



(13) BERITOPP, J. S. : Jr. Exper. Physiol., ix, 1916. 



(14) JENNINGS, H. S. : Behavior of the Lower Organisms, 1906. 



(15) BERITOFF, J. S. : Ibid., ix, 1916. 



(16) BERITOFF, J. S.: Ibid., ix, 1916. 



(17) SHERRINGTON, C. S.: Proc. Roy. Soc., Series B, No. 80, 1908. 



(18) GRUBER, C. M.: Am. Jr. Physiol., xliii, 1917. 



(19) ROGERS, J., COOMS, H., RAHE, J.: Am. Jr. Physiol., xlv, 1918 



(20) PRATT, F. H. : Am. Jr. Physiol., xliv, 1917. 



(21) BERITOFF, J. S.: Ibid., ix, 1916. 



