ME. Gr. J. EOMANES ON THE LOCOMOTOE SYSTEM OE MEDUSiE. 
303 
from the apex to the base of the nectocalyx, that the excitability is greater in the 
regions of the eye-specks than anywhere else in the course of the circular canal, and 
that it is greatest of all in the vesicular part of an eye-speck. Further, the radial canals 
present a higher degree of irritability than does the intermediate tissue. 
A mode of section, which I need not again describe, renders it possible to experiment 
with the view of ascertaining whether or not the specialized marginal tissue of the 
Medusae shows any indications of polarity while under the influence of the constant 
current. The inquiry, however, is attended with serious difficulties ; so that at present 
I am only able to say that although I have sometimes obtained satisfactory indications 
of kathelectrotonus, I have never obtained the slightest indications of anelectrotonus. 
With respect to Pflugee’s law, notwithstanding I have spent a great deal of time over 
the subject, the evidence is too contradictory to be depended upon. 
The contractile tissues of the Medusae, in the comparative irritability they manifest 
towards make and break, upon the whole conform to the rules which are followed by 
irritable tissues in general. 
The constant current during the time it is passing through a portion of the marginal 
tissue appears to have the power of inhibiting the spontaneous impulses to contraction 
which were previously originating in that portion ; for so long as the current continues 
to pass, such spontaneous impulses sometimes cease in the intrapolar portion of the 
marginal tissue, and are renewed as soon as the current is broken. 
Exhaustion of the contractile tissue may be easily shown by the ordinary methods, 
and in exhausted tissue, so far as the eye can judge, the contractions are slower and 
the period of latent stimulation prolonged. 
The tetanus which is caused by Faradaic electricity is of the nature of a number of 
contractions following one another in quick succession with perceptible intervals 
between them. 
Mutilated Sarsice, when stimulated by electricity or acidulated water, sometimes 
exhibit a highly peculiar and anomalous movement ; but it is unnecessary to enter 
into all the details a second time. 
With regard to chemical stimulation there is not much to say ; for in none of the 
excitable tissues of the Medusae have I found any exception to any of the rules which 
are conformed to by the excitable tissues of other animals. 
My observations on the behaviour of the Medusae in relation to thermal influences 
are omitted from the present paper. 
Concerning the physiological properties of the general contractile tissue of swimming- 
organs, I confine myself in this paper to stating the results obtained by the spiral 
mode of section figured on Plate 33. These results are as follow. Different individuals 
of the species Aurelia aurita manifest great variations in the amount of spiral section 
they endure before the contractile strip becomes physiologically separated from the 
rest of the gonocalyx. In the majority of cases the contractile strip becomes physio- 
logically separated from the rest of the gonocalyx before the spiral section has passed 
2 u2 
