PHYSIOLOGICAL ACTIVITIES OF THE PROTOZOA 77 



comes to them, and take what they can get, others are predatory and 

 go in search of food. These are the most interesting of all protozoa, 

 for they are occasionally too fastidious, apparently, to take the ordinary 

 run of the microscopic wilds, but seem to select their food with all the 

 care of a gourmand. They are usually armed with offensive weapons 

 in the form of trichocysts, which may be shot out from the surface 

 of the body, or carried javelin-like, at the extremities of projectile 

 tentacles. One of the most interesting of these types is Actinobolus 

 radians, one of the most primitive and one of the surest of hunters 

 (Fig. 24). "This remarkable organism possesses a coating of cilia 

 and protractile tentacles, which may be elongated to a length equal 

 to three times the diameter of the body, or withdrawn completely 

 into the body. The ends of the tentacles are loaded with trichocysts 

 (Entz, 1883). When at rest, 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 

 urocentrum, 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 grandindla, with its quick and jerky movements, approaches 

 the spot, the carnivore is not so peaceful. The trichocysts are dis- 

 charged with unerring aim, and the halteria whirls around in a 

 vigorous, but vain, effort to escape, then becomes 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." (Calkins, The Protozoa, p. 50.) 



The complicated processes involved in this act of food-getting would 

 certainly justify an Ehrenberg in the belief that actinobolus is capable 

 of wilful actions to a certain end, and that in the apparent choice of 

 food, and skill in bringing it down, it shows a high order of intelligence. 

 It would be a natural tendency to interpret such activities in terms of 

 our own consciousness, but it is much more probable that simple 

 physical or chemical laws of attraction are at the bottom of it all, 

 halteria possessing an attraction for the darts of actinobolus analo- 

 gous to that between an iron filing and a magnet, or between various 

 chemical elements. 



In all of the above cases solid food is taken into the body of the 

 protozoon and there disintegrated and digested. Many other protozoa 

 have no mouth opening nor chroma tophores to manufacture their 

 food, but absorb it through the general surface of the body, as does a 

 tapeworm. Such protozoa, like some of the lower plants, are sapro- 

 phytes and get their nutrition in the proteid matter from disintegrating 



