H J. PAUL VISSCHER. 



positively demonstrated in only a very few forms, while in general 

 it would appear that most workers have supported the opposing 

 view. 



There are only a few incidental references in the literature to 

 the feeding habits of Dileptus gigas. Biitschli ('89) says its food 

 is " sehr grob," and is quoted by Calkins as saying that it feeds 

 on ciliates alone. According to Wrzesniowski ('/o), "Dileptus 

 gigas is a voracious animal which feeds only on living food, preying 

 especially on Stylonychia." Pritchard ('61) says it feeds largely 

 on green monads, because of which it is often of a green color. 

 Hausman ('17) says "Dileptus is surely the king of beasts among 

 the ciliated protozoa. It is entirely carnivorous and its appetite is 

 apparently insatiable. The prey is stung by well-developed tricho- 

 cysts, and if too large to be swept into the buccal cavity by the cilia, 

 it is forced in by the writhings of the neck" (proboscis). 



It is clearly evident that there are a number of different views 

 concerning the feeding habits of this infusorian, all of which are 

 apparently based on purely incidental observations. Does Dileptus 

 feed on ciliates alone, or even on living food only, which would 

 involve the power of choice of food? Does it paralyze its prey 

 by means of trichocysts? What is the nature of these structures? 

 These are the problems which are considered in the observations 

 and experiments which comprise the material presented in this 

 paper. 



The work was begun at the suggestion of Professor S. O. Mast, 

 to whom I am deeply indebted for many helpful suggestions con- 

 cerning the experiments made and for much valuable criticism dur- 

 ing the preparation of this paper. 



2. MATERIAL AND METHODS. 



Dileptus gigas is one of the holotrichous ciliates belonging to the 

 family Tracheliidse. It is one of the largest of the more common 

 protozoa, often measuring over 600 micra in length. It possesses 

 an elongated body, sharply pointed at the posterior end, and at the 

 anterior end drawn out into a long proboscis which is frequently 

 as long as the body itself. The mouth opening is located at the 

 basal end of this proboscis, and has a circular aperture with a short 

 funnel-shaped gullet leading from it (Fig. i). Both these struc- 



