ME. G. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDTTS2B. 
183 
respectively; and as it must be considered in the last degree improbable that all these 
coincidences are accidental, I conclude that the effects of temperature on the natural 
rhythm of Medusae (and so, in all probability, on the natural rhythm of other ganglio- 
muscular tissues) are for the most part exerted, not on the ganglionic, but on the 
contractile element. 
(o.) In order to test the effects of gases on the artificial rhythm, I took a severed 
quadrant of Aurelia, and floated it in sea-water with its muscular surface just above 
the level of the water. Over the tissue I lowered an inverted beaker filled with the 
gas, the effects of which I desired to ascertain, and by progressively forcing the rim of 
the beaker into the water I could submit the tissue to various pressures of the atmo¬ 
sphere of the gas I was using. By an appropriate arrangement the electrodes passed 
into the interior of the beaker, and could then be manipulated from the outside, so as 
to be properly adjusted on the tissue. In this way I was able to observe that different 
gases exerted a marked influence on the rate of the artificial rhythm. My experi¬ 
ments, however, in this connexion are not as yet complete ; so I shall now confine 
myself to saying that an atmosphere of oxygen appears to accelerate the artificial 
rhythm, while an atmosphere of carbonic acid certainly retards it—the rate of the 
rhythm in air being in both cases taken as the standard of comparison, and the inten¬ 
sity of the faradaic stimulation remaining constant throughout the three observations. 
The following table gives the ratios in the case of one experiment:— 
Rate of artificial rhythm, T , ..., 
J In oxygen. In carbonic acid, 
m air. J ° 
36 per minute. 50 per minute. 25 per minute. 
It may here be observed that, to produce these results, both carbonic acid and 
oxygen must be considerably diluted with air; for otherwise they have the effect of 
instantaneously inhibiting all response, even to the strongest stimulation. When this is 
the case, however, irritability returns very soon after the tissue is again exposed to 
air or to ordinary sea-water. But I desire it to be distinctly understood that the 
results of my experiments on the influence of oxygen, both on the natural and on the 
artificial rhythm, have proved singularly equivocal; so that as far as this gas is con¬ 
cerned further observations are required before the above results can be accepted as 
certain. 
(p.) I have still one other observation of a very interesting character to describe, 
which is closely connected with the current views respecting ganglionic action, and 
may therefore be more conveniently considered here than in any other part of this 
paper. In my first paper I stated that in no case had I observed the manubrium, or 
polypite, of a Medusa to be affected, “ as to its natural motions,” by removal of the 
periphery of the swimming-bell. This statement still remains true ; but in the case of 
Sarsia a very interesting change occurs in the polypite soon after the nectocalyx has 
been paralyzed by excision of its margin. Unlike the polypites of most of the other 
