46 EDWARD C. DAY 



MATERIALS AND METHOD 



Ascidia mentula was the tunicate employed throughout the 

 present investigation. 



The body of Ascidia mentula is transparent enough as a rule 

 to permit the heart to be seen when the animal is placed on its 

 side in a vessel of sea-water and viewed through a binocular 

 microscope. In order to observe it more readily, however, a 

 slice was shaved off the tunic after a record had been made of 

 the normal beat. This operation itself temporarily affected the 

 rate, and a day was allowed to elapse for the heart to regain the 

 normal before observations were continued. New records were 

 then made of the normal condition, following which the heart 

 was cut off from all communication with the ganglion either by 

 severing the nerves or by extirpating the ganglion. 



The pulsation-waves were recorded on a kymograph by tick- 

 ing a Morse key every time a pulsation wave traveled beneath 

 an arbitrarily chosen landmark on the sliced area of the tunic. 

 With the aid of a metronome a time-curve in seconds was 

 recorded directly beneath the heart-curve. 



The temperature of the water in the vessel in which the 

 tunicate lay fluctuated a degree or two with changes in the 

 room temperature, but these slight variations had no measurable 

 effect on the beat of the heart. 



The records for a given animal extended over a period of from 

 five to ten days. During this period the tunicates were kept 

 in large aquaria provided with running sea-water. Whereas a 

 mild form of stimulation, such as tactile, might be suspected of 

 affecting the heart reflexly, attention was directed to extreme 

 methods of stimulation first to determine whether they had any 

 effect on the character of the beat. After first considering the 

 features of the normal beat, the results of strong stimulation by 

 cutting into the tunic, severing nerves, excising the ganglion and 

 amputating a siphon will be presented. 



