52 



THE PROTOZOA 



sharper tentacles, and its fluid endoplasm passes in a current down 

 the cavity of the tentacle and into the endoplasm of the suctorian. 

 In other cases, the endoplasm of the tentacle passes into the body of 

 the prey and there digests the internal substance in situ, the digested 

 parts flowing back into the body of the minute carnivore. A similar 

 mode of food-taking occurs in some Heliozoa (Vampyrella), where 

 the parasite p.enetrates the cells of algas and there digests the proto- 

 plasm. 



In all Protozoa, digestion is accomplished within the endoplasm. 

 The ingested proteid is contained within a gastric vacuole filled 

 primarily with water, which is taken in with the food. The water, 

 however, gradually changes by osmosis with the fluids of the plasm ; 



B 



Fig. 20. — Tentacles of Suctoria. [Hertwig.] 

 A. Seizing tentacles of Ephelota. B. Feeding and seizing tentacles of Ephelota. 



among these is a digestive, acid fluid, which reduces the digestible 

 portions of the food probably to some form of peptone. Then, again 

 by osmosis, the digested portions are assimilated in all parts of the 

 endoplasm. The indigestible remains of the food are excreted in 

 various ways. Sometimes, as in the Rhizopoda, they are voided 

 from any portion of the body, usually, however, from that part which 

 at the time is posterior. The gastric vacuole, after the contained 

 food has been digested as far as possible, frequently becomes a 

 defecatory vacuole, and its contents are expelled to the outside at the 

 posterior end of the individual. Finally, a distinct and permanent 

 anal opening is found in the more complex ciliates. 



2. Excretion. 



Like all other animals, the protozoon uses a certain amount of pro- 

 toplasm in the performance of its vital activities. In a large number 



