NERVOUS SYSTEM OF TUNICATE 49 



abrupt retardation of beat at the close of the series. If plotted 

 as a curve the result would take the form of a skew curve with 

 a gradual ascent and an abrupt descent. 



In graph 18^, in which the ventrad series has been length- 

 ened as a result of injury, the series of figures 45, 46, 44, 44, 44, 

 45, 45, 46, (60) would yield a more nearly symmetrical curve, 

 showing that the acceleration had had time to develop to 

 a maximum and decline before its development was cut short 

 by a reversal, 



OPERATIONS AND THEIR EFFECT ON THE BEAT 



The operations performed on the animal;^ consisted in slicing 

 away the tunic over the region of the heart, making incisions for 

 the purpose of severing the visceral nerve strand, and extirpat- 

 ing the gangHon. All of these procedures result in a lengthen- 

 ing of the pulsation series by increasing the number of beats. 

 Furthermore, the rate of beat is increased about 20 per cent; 

 ventrad and dorsad series follow each other at shorter inter- 

 vening intervals; and the acceleration which was only mildly 

 expressed in the graphs for the normal beat, crops out strongly 

 as a result of the vigorous stimulations from the operations. 



Graph 18^ exhibits all four of these phenomena as a result of 

 slicing away a part of the tunic. The animal previously (three 

 days before) had the ganglion removed, and consequently had 

 not entirely recovered, but the effect of the slicing is apparent in 

 the ventrad series where the series has been lengthened from 

 68 to 81 beats, the initial rate has dropped from 51 to 45 seconds 

 for the first 10 beats and the rate in the middle has become 10 

 per cent faster than it is at either end. This happens to be the 

 only graphic record made for the effects of slicing the tunic. 

 The operation was usually performed at the beginning of the 

 investigation in order to render the heart more visible for making 

 the records. From unrecorded observations, however, I can 

 confirm the results of this single graphic record. 



The result of severing nerves is seen in graphs 15^ and 18% 

 If the ventrad series of these is compared with the ventrad series 

 of those of the preceding normal graphs, 15^, 15-, and 18^, the 



