THE BEHAVIOR OF OTHER INFUSORIA 



119 



debris to the tip of a fine glass rod, and allowing this to touch the disk 

 of Stentor, then drawing it gently to one side. The Stentor follows it, 

 often bending far over (Fig. 83). The animal may thus bend in any 

 direction — to the right, to the left, or toward oral or aboral side. 



When infusoria are in contact with solids, their behavior always be- 

 comes much modified. The spiral movement of course ceases, and the 

 reaction to many stimuU — especially such reactions as depend largely 

 on the spiral movement — either cease or become changed. Animals 

 that when free place the axis of swimming in line with gravity, usually 

 take up, when in contact with solids, 

 any position without reference to 

 gravity. To high temperatures at- 

 tached specimens respond much less 

 readily than do free swimming ones. 

 Stentor caruleus responds readily to 

 Hght when free swimming, directing 

 its anterior end away from the 

 source of light; when attached, it 

 does not react in this way. Many 

 infusoria show a modified reaction 

 to the electric current when in con- 

 tact with solids. The flagellates 

 Chilomonas, Trachelomonas, Poly- 

 toipia, and Peridinium react readily to 

 the electric current when free swim- 

 ming; not at all when in contact 

 (Putter, 1900, p. 246). Most cihates when in contact with solids react 

 less readily to the electric current, and frequently when the reaction 

 does occur, it is of a different character from usual. While free speci- 

 mens place themselves in Une with the current, attached infusoria often 

 take up a transverse or oblique position with the peristome or oral 

 side directed toward the cathode, — just as happens in Paramecium. 

 This is true in general for the Hypotricha. 



What is the cause of the interference of the positive contact reaction 

 with the reaction to other stimuH ? It is necessary, as we have seen in 

 our discussion of this reaction in Paramecium, to distinguish two factors 

 in the contact reaction; one physical, the other physiological. The 

 physical factor is found in the fact that the organism actually adheres 

 to the surface of the sohd, — in many cases, at least, by means of a 

 mucous secretion. This physical adhesion would of course tend to pre- 

 vent that rapid movement under the influence of a stimulus which is 

 shown by free individuals. Thus, the animal might attempt to react 



Fig. 83. — • Stentor rceselii bending over to 

 remain in contact with a slired of debris 

 which is pulled by the experimenter to the 

 right. 



