LIGHT AND MOVEMENT 



response which decays with time as the organism becomes adapted. It 

 follows that if travel in a certain direction exposes it to an increase in 

 the intensity of light, the direction is changed by an increase in the 

 rate of automatic turning and the worm eventually arrives in a 



37 



Fig. 14. — Klinokinesis in a Motilk Organism. 



Track of Dendrocalum. At the upper part of the figure illumination was 

 turned on ; turning movements are rapid. As their frequency decreases the 

 path of the organism tends to straighten out so that it moves to an area of 

 shadow. The velocity remains constant all the time ; the cross-lines mark half- 

 ininute intervals (after Ullyott, 1936). 



haphazard way at the darker end of a gradient where a crowd tends to 

 aggregate ; moreover, if it crosses from a dark region into an area of 

 bright illumination, an immediate increase in the rapidity of turning 

 renders it very probable that its re-entry into the dark is speedy. It is 

 interesting and significant that the reactions of this organism seem to 

 have a sensitivity to light resembling that of the human eye (Pirenne 

 and Marriott, 1955). 



Bonner, Clarke, Neely and Slifkin. J. cell. 



comp. Physiol., 36, 149 (1950). 

 Bovie. Biol. Aspects of Colloid and 



Physiol. Chem., London (1926). 

 Brecher. Z. vergl. Physiol., 10, 497 (1929). 

 Cole. J. gen. Physiol., 5, 417 (1923). 



Davenport. E.rperimental Morphology, 



N.Y., 1, (1897). 

 Ehrenberg. Die Infusionsthierchen als 



volk. Organismen, Leipzig (1838). 

 Engelmann. Pfliigers Arch. ges. Physiol., 



19, 1 (1879). 

 Folger. J. exp. Zool., 41, 261 (1925). 



