86 



PROTOZOOLOGY 



held there on account of the viscid nature of the pseudopodium. The 

 sudden immobihty of active organisms upon coming in contact with 

 pseudopodia of certain forms, such as Actinophrys, Actinosphaer- 

 ium, Gromia, Elphidium, etc., suggests, however, probable discharge 

 of poisonous substances. In the Suctoria which lack a cytostome, the 

 tentacles serve as food-capturing organellae. The suctorial tentacle 

 bears on its distal end a rounded knob which, when it comes in con- 

 tact with an actively swimming ciliate, stops the latter immediately 

 (Parapodophrya typha, Fig. 329, a). The prehensile tentacles of 

 Ephelotidae are said to be similar in structure to the axopodia, in 



Fig. 33. Rhizopodia of Lieberkiihnia, capturing and digesting 

 Colpiditun colpoda (Verworn). 



that each possesses a bundle of axial filaments around a cytoplasmic 

 core (Roskin). These tentacles are capable of piercing through the 

 body of a prey. In some suctorians, such as Choanophrya (Fig. 334, 

 a), the tentacles are said to be tubular, and both solid and liquid 

 food materials are sucked in through the cavity. The rapidity with 

 which tentacles of a suctorian stop a very actively swimming ciliate 

 is attributed to a certain substance secreted by the tentacles, which 

 paralyses the prey. 



In the cytostome-bearing Mastigophora, the lashing of flagella 

 will aid in bringing about the food particles to the cytostome, where 

 it is taken into the endoplasm. In the ciliates there are numerous 

 types of cytostomes and associated organellae. But food-capturing 

 seems to be in general of two kinds. When the cytostome is perma- 

 nently open, the organism ingests food particles which are small 

 enough to pass the cytostome and cytopharynx, as in the case of 

 Paramecium. Another type is one, such as noted in Coleps, Didi- 



