io8 



S. O. MAST. 



which is attempting to prey upon it, the trichocysts will of course 

 be discharged from the injured region. But whether they really 

 serve for defence seems questionable. Certainly the infusorian 

 Didiniuni, which is the chief enemy of Paranicciuni, is not hin- 

 dered in the least from seizing and devouring the animal by the 

 discharge of trichocysts. It is possible that the discharge is 

 really an expression of injury a purely secondary, even patho- 

 logical, phenomenon, like the formation of vesicles on the sur- 

 face of an injured specimen." 



It would be of the greatest interest to study the feeding habits 

 of Actinobolus, with special reference to the function of tricho- 

 cysts, in the light of our present knowledge of their function in 

 Paramecium. 



MECHANICS OF SWALLOWING. 



It is well known that Didinia can capture and swallow organ- 

 isms which are relatively enormous in size. But it is difficult to 

 obtain the maximum differences in size between the enemy and 

 the victim, for both swim so rapidly that it is impossible to 



16 



c.v. 



14 15 17 



FIGS. 14, 15, 1 6 and 17. Different stages in the process of the swallowing 

 of large Paramecia by small Didinia. See text. D, Didiniuni; P, Para- 

 mecium; 11, nucleus; c.r.. contractile vacuole ; iv.v., water vacuole. 



