182 BEHAVIOR OF THE LOWER ORGANISMS 



A set of phenomena that is deserving of careful study for its implica- 

 tions as to the nature of behavior is that involved in the activities pre- 

 liminary to conjugation. It is possible that the organisms are in a 

 modified physiological condition at this time, behaving differently from 

 usual. Critical observations on this subject, of such a nature that we 

 can use them for our present purpose, are too few in number to make 

 possible a unified account of these phenomena. An account of the 

 facts for Paramecium is given on page 102. The field is one deserving 

 of much further work. 



3. FOOD HABITS 



The food habits of the infusoria are among the most interesting of 

 their activities to the student of animal behavior. As to their food habits, 

 we can with Maupas (1889) divide the infusoria into two classes. The 

 first includes those that bring the food to the mouth by means of a 

 vortex produced by the peristomal cilia ; the second those that go about 

 in search of food, seizing upon it with the mouth, like a beast of prey. 

 The former live chiefly upon minute objects, the latter upon larger or- 

 ganisms. There is, of course, no sharp distinction between the two 

 classes. Most of the infusoria with strong vortices move about more or 

 less in search of food, and most of those that seize upon their prey after 

 a search are aided by a more or less pronounced vortex. Thus the 

 roving or searching movements and the vortex are factors common 

 to the food habits of most of the infusoria. The positive contact re- 

 action further plays a most important part in obtaining food. 



Those species that depend primarily upon the ciliary vortex for 

 obtaining food usually feed upon bacteria and other minute organisms 

 and upon finely divided organic matter, bits of decaying plant or 

 animal material. Of this class of organisms Paramecium and Stentor 

 are types. In some, as in Paramecium, the food is limited to most 

 minute bodies, such as bacteria and small algae. Stentor and others 

 may take larger objects. Other infusoria and even rotifers of a con- 

 siderable size are often seen embedded in the internal protoplasm of 

 Stentor. Such animals are caught in the strong ciliary vortex, carried 

 to the buccal pouch, which often contracts in such a way as to prevent 

 their escape, and are then taken through the mouth into the internal 

 protoplasm. 



How do these organisms succeed in getting the food that is fitted for 

 them ? Is there a selection of food, and how is it brought about ? Much 

 of the difficulty as to the selection of food is solved by the conditions 

 under which these animals usually live. They are found as a rule in 



