CHAPTER X 



MODIFIABILITY OF BEHAVIOR IN INFUSORIA, AND BEHAVIOR 

 UNDER NATURAL CONDITIONS. FOOD HABITS 



I. MODIFIABILITY OF BEHAVIOR 



We have seen that in Paramecium the behavior varies to a certain ex- 

 tent in different individuals or under different conditions. Similar varia- 

 tions might be described for other free swimming infusoria. But these 

 observations do not tell us whether the behavior may change in the same 

 individual or not. Does a given individual always react in the same 

 way to the same stimulus under the same conditions? Or may the 

 individual itself change, so that it behaves differently even when the 

 external conditions remain the same, — as we know to be the case in 

 higher animals? To answer these questions it is necessary to follow 

 continuously the behavior of a single individual, and this can be done 

 most satisfactorily in attached organisms, such as Stentor and Vorticella. 

 We shall base our account on the usual behavior of Stentor rceselii, which 

 illustrates well the points in which we are at present interested. 



Stentor rceselii Ehr. (Fig. 109) is a colorless or whitish, trumpet- 

 shaped animal, consisting of a slender, staMike body, bearing at its 

 end a broadly expanded disk, the peristome. The surfcice of the body 

 is covered with longitudinal rows of fine cilia, while the edge of the disk 

 is surrounded by a circlet of large compound peristomal cilia or mem- 

 branellae. These make a spiral turn, passing on the left side into the 

 large buccal pouch, which leads to the mouth. The mouth thus lies 

 on the edge of the disk, nearly in the middle of what may be called the 

 oral or ventral surface of the body. The smaller end of the body is 

 known as the foot; here the internal protoplasm is exposed, sending 

 out fine pseudopodia, by which the animal attaches itself. 



Stentor rceselii is usually attached to a water plant or a bit of debris 

 by the foot, and the lower half of the body is surrounded by the so-called 

 tube. This is a very irregular sheath formed by a mucus-hke secretion 

 from the surface of the body, in which are embedded flocculent materials 

 of all sorts. It is frequently nearly transparent, so as to be almost in- 

 visible. Stentor rceselii is found in marshy pools, where much dead 

 vegetation is present, but where decay is taking place only slowly. 



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