88 



PROTOZOOLOGY 



down to one end of the macronucleus and then move close to its 

 concave surface to near the anterior end of the nucleus where def- 

 ecation to the vestibule takes place (Fig. 34). 



As stated above, in a number of species the food organisms are 

 paralyzed or killed upon contact with pseudopodia, tentacles or 

 exploded trichocysts. In numerous other cases, the captured or- 



FiG. 34. Diagram showing the digestion within the food vacuoles in 

 Carchesium polypimim (Greenwood), a, digestion area; b, region of 

 little change; c, region of acid reaction; d, region of neutral reaction; 

 e, defecation area. 



ganism is taken into the food-vacuole alive, as will easily be noted 

 by observing Chilomonas taken in by Amoeba proteus or actively 

 moving bacteria ingested by Paramecium. But the prey ceases to 

 move in a very short time. Apparently some substances are se- 

 creted into the food vacuole by the protoplasm of the organisms 

 to stop the activity of the prey within the food vacuole. Engel- 

 mann (1878) demonstrated that the granules of blue litmus, when 

 ingested by Paramecium or Amoeba, became red in a few minutes. 



