Mast, Orientation in Euglena with some Remarks on Tropisms. (549 



it ought to give the shock-reaction if the light intensity in the 

 field is suddenly reduced, but not if it is increased. If the organism 

 is negative precisely the opposite should occur. There should, in 

 other words, be a strict correspondence in every condition of 

 illumination and physiological state between orientation and shock- 

 reactions. When individuals orient negatively they ought to respond 

 with the shock-reaction if the light intensity in the field is sud- 

 denly increased, not if it is decreased. When they orient positively, 

 on the other hand, they ought to respond with the shock-reaction 

 if the intensity is suddenly decreased not if it is increased ; and 

 when they do not orient at all they ought not give the shock- 

 reaction to either an increase or a decrease in intensity. 



The subject matter under four of the eight headings mentioned 

 (A, B, C and F) deals with this correspondence. 



As a general result of his observations Bancroft maintains 

 that in a number of instances the agreement between shock-reactions 

 and orientation demanded by the change-of-intensity theory as 

 described above was not found. His most important results regard- 

 ing this matter are visualised in the following diagrams. 





Culture. 



HEL. H- + + + + + + H- + + QQQQ- 



S. -M. S S S S B S SBSSSSSBSSOIII F 



HEL. OQOOOOOOO 

 "STMT OOOOOOOOOOOOOOOI I II IF 



(From Bancroft, p. 400, Fig. 4.) "Diagram to show the correlation between 

 the sign of the heliotropism and the character of the shock-movements. Distances 

 a long the horizontal line indicate distances from the light. On the left, then, we 

 have a weak light and on the right a strong light. Above the line is indicated 

 the sign of the heliotropism (Hel.). Below the line is indicated the character of 

 the shock-movements (S. M.). S = shock-movements produced by sudden shading, 

 and not by sudden illumination; I = shock-movements produced by sudden illumina- 

 tion, and not by sudden shading; F =. shock-movement mechanism becomes fatigued 

 if light lasts for half an hour or an hour; O == absence of reaction; B = correla- 

 tion in Culture B; A = correlation in ordinary individuals of Culture A; Lower 

 A correlation in exceptional samples of Culture A in which the shading reaction 

 appeared; C = correlation in exceptional sample from Culture B." 



These diagrams indicate that in addition to what the change- 

 of-intensity theory demands, he obtained (1) shock-reaction when 

 there was no orientation, (2) negative orientation in individuals 

 which gave shock-reactions to decrease of intensity; (3) negative 

 orientation in individuals which did not respond either to sudden 



