NERVOUS SYSTEM OF TUNICATE 51 



intervening interval. In the dorsad series of both 16^ and 18^ 

 and in both ventrad and dorsad series of 15" there is a retarda- 

 tion of rate after the initial acceleration with a subsequent speed- 

 ing up before the final slowing down. This is exhibited best by 

 graph 15« in the ventrad series 43, 44, 1^8, 47, 47, 46, 4^, (50) and 

 in the dorsad series 43, 44, 43, 41, Jf2, (47), the places of retarda- 

 tion being indicated in italics. The figures in parentheses repre- 

 sent the calculated number of seconds for the incompleted last 

 10 beats and they indicate that the final rate was slower than at 

 any other place in the series. 



From these results it is evident that the three operative pro- 

 cedures of paring away the tunic, severing the nerves and extir- 

 pating the ganglion, bring about in lesser or greater degree the 

 same alteration of the characteristics of the dorsad and ventrad 

 series of beats : an increase in the number of beats, a primary and 

 secondary phase of acceleration through the series, a shortening 

 of the interserial pauses, and a lengthening of the time of the 

 series more or less directly in proportion as the number of beats 

 is increased and their frequency accelerated. 



When, however, the more profound operation of amputating 

 the oral siphon is carried out subsequent to the removal of the 

 ganglion, as was the case for graph 18^, the above results occur 

 in a considerably modified form. The accelerative effect is 

 more strongly expressed here than in any of the preceding graphs, 

 but the number of beats is incommensurately small. Mark, 

 for example, how the rate for the initial 10 beats gradually 

 increases with each succeeding injury: from the normal 53" in 

 the ventrad series of 18^ it drops to 51" in 18-, to 50" in 18^, 

 to 45" in 18^ and to 44" in 18^ Now, up to the third injury in 

 18" there is a concomitant increase in the number of beats from 

 the normal number 39 in 18^ to 54 in 18-, to 65 in 18% to 81 in 18^ 

 but in 18^ they drop back to 65. One would have expected, from 

 the way the acceleration of rate continued to increase, that the 

 number of beats would here have jumped from 81 to about 85, 

 but instead it drops back to 65 a figure corresponding to an initial 

 rate of acceleration per first 10 beats exhibited by 18^ In the 

 dorsad series this drop is even more pronounced: the 22 beats 



