102 



PROTOZOOLOGY 



tive tubule" beginning with the cytostome and ending in the cyto- 

 pyge, and the food vacuoles travel through it. Cosmovici (1931, 

 1932) saw such a canal in soluble starch-fed Colpidium colpoda upon 

 staining with iodine, but Hall and Alvey (1933) could not detect 

 such a structure in the same organism. Kitching (1938b) observed 

 no such tubule in the peritrichous ciliates he studied, and concluded 

 that the food vacuoles are propelled over the determined part of the 

 course by the contraction of surrounding cytoplasm. In Vorticella 

 sp., food vacuoles are formed one by one at the end of cytopharynx, 

 migrate through different parts of the cytoplasm without order and 

 food material is digested (Fig. 37, a). Old food vacuoles are defecated 

 through a small papilla on the lower wall of the cytopharynx and 

 thence to the outside (Hall and Dunihue, 1931) (Fig. 37, b-d). 



^r\ 



n tr\ n n 



Fig. 36. Ingestion of brine by Rhopalophrya salina (Kirbj'). 



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

 paralyzed or killed upon contact with pseudopodia, tentacles or ex- 

 ploded trichocysts. In numerous other cases, the captured organism 

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

 serving Chilomonas taken in by Amoeba proteus or actively moving 

 bacteria ingested by Paramecium. But the prey ceases to move in a 

 very short time. It is generally believed that 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. Engelmann 

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

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

 (1881) examined the staining reactions of amoebae by means of 

 haematoxylin, and found that the watery vacuoles contained an 

 acid. Metschnikoff (1889) also showed that there appears an acid 

 secretion around the ingested litmus grains in Mycetozoa. Green- 

 wood and Saunders (1894) found in Carchesium that ingestion of 



