NERVOUS SYSTEM OF TUNICATE 57 



graph 15-. After severing the nerves, however, the number of 

 beats after soaring to 126 returned to 23, and when the whole 

 ganghon was removed it rose to 54 and subsided to 28. In this 

 instance the recovered condition exhibits a number of beats 

 which is above the normal and it stands in contrast to the re- 

 covered condition for animal no. 15, where the number of beats 

 was below the normal. 



One may therefore just as legitimately ask whether this super- 

 normal number of beats after recover}^ is likewise not an ex- 

 pression of lifted ganglionic control. 



In the absence of conclusive evidence from the study of the 

 dorsad series, one can only balance the two cases one against the 

 other, pointing out that animal no. 15 recovers at best to a number 

 of beats only two above the lowest recorded normal, while animal 

 no. 16 recovers at best to a number six below the lowest recorded 

 normal. But in view of the fact that the normal number fluctu- 

 ates through a recorded range of 8 beats for no. 16 and 4 beats 

 for no. 15, the two cases of recovery may be regarded as close 

 enough to the normal to be within the range of normal fluctua- 

 tion. This is substantially confirmed by the instances pointed 

 out in the records of the ventrad series where the number of 

 beats upon recovery coincides exactly with the normal number. 

 Animal no. 15 shows this precise readjustment both after sever- 

 ance of nerves between ganglion and heart and after extirpation 

 of the ganglion: three times the heart upon recovery exhibits the 

 same number of 25 beats which it exhibited prior to the opera- 

 tions. Animal no. 16 twice shows a state of recovery in which 

 the number of beats tallies with the normal record of 21. 



Consequently, since there is not only the close approximation 

 to the normal number of beats upon recovery in the dorsad 

 series, and also an exact tally with the normal upon recovery in 

 the ventrad series, the feature of the number of beats gives no 

 evidence of any regulatory control exerted by the ganglion on the 

 heart. 



The manifestation of fluctuations in the number of beats 

 about a certain normal both for the uninjured and the injured 

 state of the animal suggested the possibility that the range of 



