G14 EAYMONTJ PEARL. 



away from tlie stimulus (negative reaction) is due to a 

 lengthening of the side stimulated. 



It may possibly be objected to the last experiment that 

 the impulse from a stimulation at, for example, B (Fig. 21) 

 took the path indicated by the dotted line in that figure, and 

 caused a contraction on the left side of the bod}', so that 

 really the observed turning was the result of a contraction on 

 the side opposite that stimulated. To this objection it may 

 bo answered that by stimulating different points along the 

 edge B it is possible to cause the point about which the 

 turn occurs as a pivot to be located anywhere along the line a- y. 

 It is very evident that contraction of muscles in the region N 

 can have nothing whatever to do with turning of the right 

 piece about the point x. So this objection is without force. 



As the process of regeneration of a cut longitudinal half of 

 the body goes on, the piece will straighten out from the 

 curved form it takes after the cut is made, and it is conse- 

 quently possible to obtain specimens in which the regenera- 

 tion of the missing half of the body has produced only a very 

 small amount of new tissue, and which are at the same time 

 nearly straight in outline and able to make progressive move- 

 ments. The reactions of such partially regenerated speci- 

 mens are of importance as throwing light on the normal 

 mechanism of the reactions. The reactions of a typical 

 specimen of this sort may be described in detail. On October 

 10th, 1901, a small piece of the anterior end of a specimen of 

 V. maculata was isolated. The piece was cut as nearl}' as 

 possible in the form shown in l^^ig. 22, a. On October IGth 

 the piece had the form shown in Fig. 22, h. A narrow strip 

 of new tissue had formed down the right side, and the forma- 

 tion of the outline of the head and of the right eye was just 

 beginning. At this time the reactions of the specimen were 

 as follows. Stimuli applied at y caused the head to turn 

 sharply away from the stimulus (typical negative reaction). 

 This reaction was quite like that given by a normal individual 

 stimulated in the same way. Stimulation at x, however, 

 produced no trace whatever of a negative reaction. On 



