FUNCTIONAL ACTIVITIES 



95 



by methods akin to harpooning. Here long tentacles, as in the 

 ciliate Actinobolus radians and in Suctoria, usually radiate out 

 in the water and are activated by the stimulus of a passing organ- 

 ism. Actinobolus is most interesting, for it is stimulated to 

 activity usually by only one type of food organism. This re- 

 markable organism possesses a coating of cilia and protractile 

 tentacles, which may be elongated to a length equal to three times 

 the body-diameter, or withdrawn completely into the body. The 

 ends of the tentacles are loaded with trichocysts.* When at rest 



Fig. 55— "HARPOON" METHOD OF 

 FOOD GETTING 



A ciliated protozoan, Actinobolus radians, which 

 lies mouth down, in wait for prey. The ends 

 of the spine-like tentacles hold a bit of poison 

 which is inoculated into a small organism like 

 Halteria if it strikes against them. The prey 

 is paralyzed and is then drawn around to the 

 mouth by shortening of the tentacles and action 

 of the cilia 



After Moody 

 Magnification, 275 



(Fig. 55) the mouth is directed downward, and the tentacles 

 are stretched out in all directions, forming a minute forest of 

 plasmic processes, among which smaller ciliates, such as Urocen- 

 trum, Gastrostyla, etc., or flagellates of all kinds, may become 

 entangled without injury to themselves and without disturbing 

 the Actinobolus or drawing out the fatal darts. When, however, 

 an Halteria grandinella, with its quick and jerky movements, 

 approaches the spot, the carnivore is not so peaceful. The 

 trichocysts are discharged with unerring aim, and the Halteria 

 whirls around in a vigorous, but vain, effort to escape, then be- 

 comes quiet, with cilia outstretched, perfectly paralyzed. The 

 tentacle, with its prey fast attached, is then slowly contracted 

 until the victim is brought to the body, where, by action of the 

 cilia, it is gradually worked around to the mouth and swallowed 

 with one gulp. Within the short time of twenty minutes I have 

 seen an Actinobolus thus capture and swallow no less than ten 

 Halterias. 



♦Trichocysts are minute stinging organs (see Fig. 48, page 83). 



