| of Torpedo ocellata. 173 
The lever connected with the wheel is arranged to write under 
‘that recording the amplitude of the movements. It gives a record 
‘showing the number of movements which have occurred during 
a period of 52 seconds in each minute and at the same time 
provides a time tracing in minutes by which the upper tracing 
may be read. 
The general arrangement of the apparatus is shown in Fig. 3. 
Records are taken on a drum moving about 10 cms. per hour, and 
thus quite a short tracing shows at a glance the frequency and 
amplitude of the movements over periods of several hours. ‘T'wo 
sources of instrumental error must be noted, though they do not 
affect any of the conclusions to be drawn from the experiments to 
be described. In the first place variations in frequency within 
the interval of 52 seconds would escape notice in the record if 
they chanced to include an acceleration and a retardation which 
exactly balanced one another. In the second place, when the 
frequency of the movements is quite regular, there is liable to be 
@ variation of one in the record from minute to minute, since the 
number of movements will not as a rule be an exact sub-multiple 
of the number of seconds during which they are counted. 
Examples of the records obtained are shown in Figs. 4 and 5. 
The method is obviously suitable for the study of the heart beat 
or for counting drops. 
Experiments were made on moderate sized specimens of 
Torpedo ocellata. The fish was held lying with the ventral 
surface uppermost by means of von Uexkiill’s device. A gentle 
stream of sea-water was led into the mouth by a rubber tube. 
The fish was placed in a small tank, provided with an overflow 
pipe, and as a rule was covered with water. The recording lever 
was connected by a thread to one of the gill clefts. 
The temperature of the water varied in different experiments 
from 18° to 22° C. ; 
Observations. After the irregularity caused by the manipula- 
tion involved in fixing the fish in position, the respiratory 
movements became regular, and often continued so with little 
change in amplitude or frequency for several hours. During this 
period it was very usually found that the fish made occasional 
spouting movements. 
The graphic records showed that these spouting movements 
tended to recur at fairly regular intervals. 
Fig. 4 is an example taken from the close of a period of two 
hours during which the behaviour had been practically the same 
the whole time. It is to be noted that the spouting movements 
do not occur at exactly equal intervals, yet sufficiently nearly so 
to suggest a slightly-distorted rhythm. The period of this rhythm 
was sometimes as great as 5 minutes—in other cases the movements 
recurred several times in a minute. 
