154 BEHAVIOR OF THE LOWER ORGANISMS 



to turn the organism toward the oral or peristomal side (Fig. 100, 6). 

 Under these circumstances, another principle requires consideration. 

 Normally the peristomal cilia strike backward. When they strike for- 

 ward, they develop much less energy, less turning power, than when 

 they strike backward. Therefore, when in the position shown at 6, 

 Fig. 100, the turning is much less rapid than in other positions, and may 

 easily be prevented by a slight resistance. These relations will be 

 understood by an examination of the diagram (Fig. 100). 



In Paramecium, as we have seen, the same condition of affairs is 

 exemplified to a certain degree, so that the organism turns toward the 



oral side in all positions save from 

 d to /, Fig. 63. In the Hypo- 

 tricha (Oxytricha and Stylo- 

 i nychia) this condition is most 

 typically exemplified. A large 

 share of the body cilia are absent 

 or have taken the function of legs, 



FIG id. Transverse (or oblique) posi- yfafa tne peristomal cilia are very 



tion and movement of Oxytricha under the A 



action of the electric current, when the animals powerful. In almost all CaSCS 



are in contact with the substratum The ^ ese organisms become oriented 

 penstome is directed toward the cathode. i i 



to the electric current by turning 



toward the aboral (right) side. It is only when the peristomal cilia are 

 squarely facing the cathode (Fig. 100, 6) that the animal may turn toward 

 the oral (left) side. In this position the peristomal cilia beat forward, 

 and all the cilia of the body aid in turning the organism toward the oral 

 side. On reaching a position with anterior end directed to the cathode the 

 peristomal cilia are directed forward, but their beating has become so weak 

 as to be almost without effect. The animal, therefore, retains this position. 

 When specimens of the Hypotricha are in contact with a surface, as 

 is usually the case, the forward beat of the peristomal cilia is often so 

 weak and ineffective in the transverse or oblique position (Fig. 100, 6) 

 that it does not turn the animal against the resistance offered by the 

 attachment of the ventral cilia. Such specimens, therefore, remain in 

 the transverse or oblique position, the anterior end usually slightly in- 

 clined toward the cathode, as in Fig. 101. In this position they run 

 forward. When the current is reversed, so that the anode lies next the 

 peristome, the powerful peristomal cilia strike backward. The ani- 

 mals, therefore, turn toward the aboral (right) side till they have again 

 become nearly transverse to the current. They then move forward in 

 the direction so indicated. Similar phenomena are at times to be ob- 

 served in other ciliates, not belonging to the Hypotricha. This is true, 

 as we have seen, even for Paramecium. 



