LIGHT AND MOVEMENT 



49 







} 



Fig. 21. — Klinotaxis in a Swimming Organism. 



The orientation of £'M5'Ze?ia I'iVfrZ/s. The orientation of the organism as it 

 swims away from the hght (coming from below) rotating in a wavy path ( 1 to 6). 

 At 6 the du'ection of the light is reversed to come from above ; each time the 

 receptor area is shielded by the pignient the organism swerves to the dorsal side. 

 After an initial wavy course (7 to 8) it bends laterally across the path of the 

 beam, and from 13 to 18 it again swims as before away from the light (after 

 Jennings, 1906). 



The Ciliates, which orientate themselves by means of ciha much 

 as a rowing boat without a rudder, react phototactically in a similar 

 manner (Fig. 22). Thus Stentor cceruleus, a trumpet -shaped ^ Protozoon, 

 the bell of which is surrounded by cilia within which is an eccentrically 

 placed mouth, exhibits the same reaction by virtue of the fact that the 

 oral surface is more photosensitive than the aboral (Jennings, 1904 ; 

 Mast, 1906-11). 



A similar arrangement multiplied many-fold is seen in colonial forms, such 

 as Volvox globator, a green organism found in fresh-water pools, formed of a 

 hollow spherical colony of some 10,000 individual zooids each of which is 

 equipped with two fiagella and a stigma protected on one side by a pigmentary 

 shield ; stimulation of the sensitive area results in the translation of the diagonal 



1 The name is from Stentor, the herald of the Iliad who had a loud trumpet-like 

 voice. 



S.O.— VOL. I. 4 



Stentor 



Volvox 



