174 Mr Mines, Note on the respiratory movements, ete. 
The frequency of the spouting movements was greatly in- 
fluenced by changes in the mechanical conditions. The effect of 
an increased flow of water through the pharynx always caused an 
increase in the frequency of the ordinary respiratory movements 
with a decrease in the frequency of the spouting movements. 
These points are illustrated by Fig. 5 (a) and (b). The tracing 
are from different experiments. 
In (a) the flow of water through the pharynx was reduce 
during the times indicated by the white horizontal lines. In (6) 
the horizontal line indicates an increase in the rate of flow. 
The frequency scale at the side applies to both tracings. 
I have not found any definite relationship between the | 
chemical composition of the water and the frequency of the | 
rhythm. <A considerable increase in the carbon dioxide tension, 
changing the hydrogen ion concentration of the sea-water from 
about 10-°* to 107* caused violent movements and upset the 
rhythm altogether. In one case increase in the oxygen tension of 
the water was accompanied by cessation of the spouting move- 
ments which returned when the oxygen tension was restored to 
its original value. This result was not confirmed on repetition 
with other specimens. Further work on the subject is needed. 
The object of the present communication is to point out that 
these spouting movements do often occur in the resting fish, 
separated by intervals so nearly alike as to make it improbable — 
that the occurrence of each movement is the result of a fortuitous — 
external stimulus. External stimuli will readily affect the reflex 
mechanism, but it appears that when external conditions are kept- 
as uniform as possible the periodicity of the spouting movements 
is determined by the central nervous system. 
I wish to express my warmest thanks to Doctor Dohrn and 
his Staff for the kindness with which they aided my work during 
my tenure of the University Table at the Stazione Zoologica in 
the autumn of 1912. 
