LIFE HISTORY OF TWO RARE CILIATES 371 



the organs in total preparations and sections, as well as in the 

 living animal examined under the oil immersion lens, I have 

 been unable to find the structures described by von Erlanger. 



With partially retracted tentacles, Actinobolus, rotating on 

 its long axis, swims occasionally near the surface of the water, 

 coming to rest from time to time with the mouth downward, 

 on the bottom of the culture dish, moored by means of the oral 

 tentacles. Gradually the retracted tentacles elongate until, seen 

 with the low power, the animal is apparently surrounded by a 

 halo of short opaque rods at varying distances from the per- 

 iphery of the body. By careful focussing, the opaque rods 

 are seen to be the tips of the tentacles which can be readily 

 traced to the cortical layer of the body. The tentacles are 

 extremely slender organs of equal thickness throughout their 

 length, the tip being slightly rounded, never pointed or knobbed. 

 The opacity of the distal end is due to a mass of minute dark 

 granules, the trichocyst material, which can be seen in circu- 

 lation as the tentacle is extended. 



As shown by Calkins, the tentacles are food-getting organs, 

 Actinobolus subsisting exclusively on Halteria grandinella; often 

 as many as four or five may be seen attached to these organs, 

 the little ciliates being carried around one by one to the mouth 

 and swallowed. It is a matter of conjecture as to the method 

 by which the capture of this prey is accomplished. Calkins 

 in his description of the action of the tentacles of Actinobolus 

 says, ('Ola, p. 657): 



The trichocyst which von Erlanger described, or its analogue (I 

 was unable to make it out as described by Erlanger), brings down the 

 prey, and the tentacle, by shortening, fetches it to the mouth. The 

 tentacle itself is inserted in Halteria, for it can be easily seen with the 

 greatest distinctness w^ien the victim becomes quiet, and I believe 

 that the dart at the end as described is not discharged into the prey 

 but is driven into the soft body of the victim as a minute spear, with 

 shaft attached. 



Since the tip of the tentacle is blunt and slightly rounded 

 it seems to me incapable of piercing the cuticle of Halteria. 

 In neither fixed nor living material have I found any evidence 

 of a dart-like structure at the tip. The tentacles appear to 



