622 SERGIUS MORGULIS 



from a number of trials that worms neither too sluggish nor ex- 

 cessively agile and irritable are best adapted for the experiment. 



The mode of reaction depends upon two circumstances; first 

 the amount of turning of the sector; secondly, the particular mo- 

 ment at which the worm passes on to the fixed plate. If the sec- 

 tor is turned to the left as soon as the anterior quarter of the worm 

 has gained the fixed plate, the worm comes to a stand-still 

 instantaneously. The suspension of activity lasts a few seconds, 

 in some exceptional instances, indeed, it lasted 45 seconds- 

 then the head of the worm changes its position with a sudden jerk 

 to the right, the entire worm being thus brought again into a 

 straight line oblique to its original direction, and the animal starts 

 moving in the new direction. If at the moment of the turning of 

 the sector to one side the worm is already half-way across, it does 

 not cease moving even for an instant, but, swerving its head to 

 the opposite side and thus assuming an S-shaped form, it con- 

 tinues upon the new path. After a while the worm's body again 

 becomes straight. Turning the tail to the right or to the left 

 in the region of the posterior third causes but a slight reaction of 

 orientation in the anterior part of the worm. 



The intensity of the orientation of the head depends upon the 

 amount of turning of the tail, being the greater the further the 

 tail is swung. It should be observed, however, that the amount 

 of turning of the head is always smaller than that of the tail. 

 Furthermore, the turning of the tail through an arc of about 20,° 

 while sufficient to cause a bending of the head in an opposite direc- 

 tion, would fail completely to produce an effect if only a small 

 portion of the tail were turned. 



To reiterate : the extent of the orientation-reaction of the head 

 is directly proportional to the length of the posterior part of the 

 worm deflected from the straight course; and, similarly, the degree 

 of deflection necessary to occasion the orientation-reaction is 

 inversely proportional to the length of the deflected tail. 



It is possible, of course, to influence the direction of the worm's 

 movements more than once, by turning the sector of the appara- 

 tus first to one side and then to the opposite side. The worm 

 may thus be forced to maneuver in a tortuous course. If a worm 



