254 SELIG HECHT 
By means of the apparatus which has been previously de- 
scribed (fig. 7), kymograph records were made of this rhyth- 
micity. Animals were allowed to register their activity at times 
of the day and night when Agar’s Island was deserted except 
for the presence of two people in a house more than a hundred 
yards from the laboratory. The curves in figures 14 and 15 
show the movements of two animals which are entirely typical 
of all the others. There can, therefore, be no doubt of the 
thythmic character of the spontaneous contractions exhibited 
by Ascidia. | 
The rhythmicity of the movements possesses a peculiarity 
which resemble the refractory properties of the vertebrate 
heart (Woodworth, ’02). It is well known that immediately 
after a contraction of the ventricle, it fails to respond to stimula- 
tion. After this refractory period, an external stimulus will 
cause a pulsation even before the expected rhythmic contraction 
is due. Similarly in Ascidia a stimulus which is so slight that 
it causes merely a siphon rim movement will, when applied 
regularly at intervals of a minute, call forth complete body 
movements at approximately the periods when they are expected 
to occur rhythmically. The following record is chosen as an 
example because the spontaneous contractions of this animal 
have already been recorded (figs. 13 and 14). 
Exp. VI.27.3. Animal in a nine liter battery jar. Stimulated every minute 
by the impact against the jar of a pendulum bob swinging from a distance of five 
centimeters. 
12:21 Siphon rim movement 
22, ““ “cc “ce 
23 “cc “ec “ 
24 “é “cc “cc 
25 Complete body movement 
26 Siphon rim movement 
PW “ “ “ec 
28 cc “ce “cc 
29 Complete body movement 
30 Siphon rim movement 
31 “ce “ “ 
32 “ “ce “ 
33 Complete body movement 
