1 84 BEHAVIOR OF THE LOWER ORGANISMS 



is outstretched and feeding quietly in the usual way. Many small 

 objects pass into the buccal pouch and are ingested. Suddenly a larger, 

 hard-armored infusorian, Coleps, is drawn into the pouch. At once 

 the ciliary current is reversed and the Coleps is driven out again. Then 

 the current is resumed in the usual direction. Vorticella and other fixed 

 infusoria often reject large objects in the same way. But besides re- 

 versing the ciliary current, these organisms may, when the ciliary current 

 brings unsuitable material, bend over into a new position, contract, 

 or leave their place of attachment and swim away. All these reactions 

 have been described in detail in our account of the behavior of Stentor. 



Thus the choice of food in all these organisms depends merely upon 

 whether the usual negative or avoiding reactions are or are not given. 

 The avoiding reaction is the expression of such choice as occurs. Look- 

 ing at the matter from this standpoint, we are forced to conclude that the 

 entire behavior involves choice in almost every detail. The animals, 

 as we have seen, are giving the avoiding reaction in a certain degree, 

 from a slight widening of the spiral course to the powerful backward 

 swimming, almost continuously. The straightforward course is the 

 expression of positive choice or acceptance; the avoiding reacting of 

 negative choice or rejection. No distinction can be made between choice 

 and the usual behavior. Indeed, choice is the essential principle of 

 behavior based on the method of trial. 



What happens if the organisms settle down and attach themselves 

 in a region where no food exists ? This question seems not to have been 

 specially investigated. But it is known that under most kinds of un- 

 favorable conditions, conditions which interfere with the normal 

 functions, the animal, after a time, leaves its place and swims away 

 to a new location. Doubtless this happens also when food is lacking. 



We may sum up the food habits of this first class of ciliates as fol- 

 lows: They settle down in a certain region and then bring a current 

 of water to the mouth. The particles in this current are taken as food, 

 without any sorting, so that many that are not useful are ingested along 

 with the others. But if decidedly unsuitable material is brought, then 

 the animal reacts as to other unfavorable stimuli reversing the cur- 

 rent, contracting, shifting position, or finally moving away to a new place. 

 The method of trial of varied movements is at the basis of the behavior 

 here as elsewhere. 



The second class of ciliates includes those which move about in search 

 of their food, preying upon larger organisms and seizing them with the 

 mouth. Maupas has well called these the hunter ciliates. The method 

 of taking food in these animals often resembles in many respects that of 

 the species already described. Thus Stylonychia runs about here and 



