NERVOUS SYSTEM OF TUNICATE 53 



tions are in decided contrast to the rate of 43, 43, 44, 48, 47, 

 47, 46, 48, 15 for the injured condition. The recovered rate of 

 the dorsad series is 51, 54, 40 as compared to 54, 55, 28 for the 

 normal, and here again the rate for the recovered and normal 

 conditions are in sharp contrast to the rate of 43, 44, 43, 41, 

 42, 19 immediately after the ganglion had been removed. 



While in graph 15^ the recovered rate did not slow down quite 

 to the normal in either ventrad or dorsad series, in graph 16^ the 

 rate of both series after recovery was a trifle slower than normal. 

 Here the ventrad series shows after recovery from the operation 

 the same number of beats, 21, as for the normal condition exhib- 

 ited by graph 16-, but these 21 beats required 6 seconds longer 

 for their completion in the recovered condition than they did in 

 the normal series. The dorsad series is also subnormally slow. 

 Since no record was made upon the day following the extirpation 

 of the ganglion for animal no, 18 no reliable statement can be 

 made regarding the character of immediate recovery. Three 

 days after the operation, however, a graphic record, 18", revealed 

 a more advanced degree of injury, as far as number of beats is 

 concerned, than did the record made immediately following the 

 operation. But whereas the number of beats had increased from 

 65 (injured ventrad series) to 68 (recovered ventrad series) and 

 from 58 (injured dorsad series) to 83 (recovered dorsad series) , 

 there was a slight recovery to a slower rate of beat for both ven- 

 trad and dorsad series, as the graphs 18^ and 18" of table 3 show. 



SUMMARY OF RESULTS 



There is a certain normal activity of the heart of the tunicate, 

 Ascidia mentula, in which the number of beats is about 25 for 

 both ventrad and dorsad series. The initial rate is 5.5 seconds 

 per beat, and the pauses between the series average about 13 

 seconds. Stimulation, such as slicing pieces off the tunic, sever- 

 ing the nerves between ganglion and heart, and extirpating the 

 ganglion, causes the number of beats to increase from 25 to 50 

 or 90, the rate to drop from 5.5 to 5 or 4.5 seconds per beat, 

 indicating acceleration, and the pauses to shorten from 13 to 

 10 or 8 seconds. In addition to these changes there is a retarda- 



