164 



STEREOTROPIC ORIENTATION 



described. This gives confirmatory proof of the machine-like charac- 

 ter of the reaction. It is also worthy of note that the circumoral 

 nerve ring plays no part in the reaction, but only the radial nerve 

 through which the tube feet receive their impulses since these experi- 

 ments can be made on isolated rays. Fig. 1 is a diagram showing the 

 orientation of the tube feet which are extended toward the point 

 of contact stimulation. 



If two points on the same side of the ray but at a distance from each 

 other are touched, then the tube feet turn to that side (Fig. 2). The 

 tube feet midway between the two loci of stimulation bend neither 

 toward the one nor toward the other but at right angles to a line 



Fig. 1. 



Fig. 2. 



Fig. 3. 



Fig. 4. 



Fig. 1. Arrows indicate the direction in which the tube feet are bent, the 

 arrow tip being put for the terminal disks. This diagram shows the tube feet 

 all inclined accurately to the locus of contact excitation indicated by the 

 U-shaped outline. 



Fig. 2. Two loci of contact excitation on the same side of the ray result in 

 the tube feet orienting themselves at right angles to the axis of the ray and to a 

 line joining the two loci of stimulation. The median tube feet do not incline to 

 either point of excitation but orient like a phototropic insect placed midway 

 between two lights of equal intensity. 



Fig. 3. Slight contact excitation has been appUed at two points on opposite 

 sides of the ray. Only the tube feet in the immediate vicinity are directed 

 toward the points of excitation. The other tube feet are directed along the med- 

 ian axis of the ray at right angles to a line joining the two loci of stimulation. 



Fig. 4. The same as in Fig. 3, except that the pressure is strongly applied re- 

 sulting in withdrawal of the tube feet in the immediate vicinity of excitation, and 

 orientation of the others to the center parallel with the axis of the ray and per- 

 pendicular to a line joining the two loci of excitation. 



