194 
MR. G. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUSA. 
from the point o in the area z z. After this origination of the contractile waves from 
the point o had been observed a great number of times, I removed the lithocyst. 
The effect was not only to prevent the further origination of contractile waves in the 
area xxxx, but also to prevent their further origination from the point o —the entire 
umbrella thus becoming paralyzed. Hence, before the removal of the lithocyst, the 
contractile waves which originated at the point o, no less than those which originated 
at the lithocyst itself, must in some way or other have been due to the ganglionic 
influence emanating from the lithocyst and asserting itself at the distant point o. 
This property which lithocysts sometimes present of asserting their ganglonic influ¬ 
ence at a distance from their own locality, can only, I think, be explained by supposing 
that at the point where, under these circumstances, the contractions originate, there 
are situated some scattered ganglionic cells of considerable functional power, but yet 
not of power enough to originate contractile waves unless re-enforced by some 
stimulating influence which reaches them from the lithocyst through the nervous 
plexus. But whether or not this is the true interpretation of the facts, I think it is 
evident that these facts are of considerable importance in relation to the theory of 
ganglionic action which has already been so fully discussed in the first division of the 
present paper. For, turning again to the woodcut (fig. 11), if the discharges of the 
lithocyst are regulated only by resistance, it seems almost unaccountable that these 
discharges should frequently fail to excite the contiguous area xxxx, wdiile they 
are effectual in exciting the remote area z z z z ; and this even after z z z z has been 
almost completely severed from xxxx by the severity of the incisions. To my 
mind, the facts seem rather to point to the conclusion that the lithocyst is engaged in 
emitting some sort of continuous ganglionic impulse which spreads throughout the 
nervous plexus, and helps to stimulate the ganglionic cells which are scattered 
throughout this plexus. And this conclusion is not incompatible with the Hew that 
the resistance which is offered by the plexus is so adjusted to the accumulation of 
energy by the lithocyst, that this energy admits of being periodically discharged in 
greater amount, just at the time when the contractile tissues have completely recovered 
from then exhaustion due to their previous contraction. In support of this interpreta¬ 
tion of the facts, it may be added that after the removal of the lithocyst I tried the 
effects of gently irritating the tissue in the area x x x x with a camel-hair pencil, 
and I found that by so doing I could again excite the origination of contractile waves 
from the point o in the area zzzz. 
§ 4. Regeneration of the excitable tissues of Aurelia aurita.—The only remaining 
facts which I have now to communicate have reference to the astonishing rapidity 
with which the excitable tissues of the Medusae regenerate themselves after injury. 
In this connexion I have mainly experimented on Aurelia aurita, and shall therefore 
now confine my remarks to this one species. 
If with a sharp scalpel an incision be made through the tenuous contractile sheet 
of the subumbrella of Aurelia, in a marvellously short time the injury is repaired. 
