MR. G-. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUSiE. 
275 
the immediate result of any particular experiment. Further, although such mutilation 
of a gonocalyx is usually followed by a paralysis as sudden and marked as that which 
follows such mutilation of a nectocalyx, the paralysis of the former differs from the 
paralysis of the latter in that it is very seldom 'permanent. After periods varying from a 
few seconds to half an hour or more, occasional, weak, and unrhythmical contractions 
begin to manifest themselves ; or the contractions may even be resumed with but little 
apparent change in their character and frequency. The condition of the animal 
before the operation as to general vigour, &c. appears to be one factor in determining 
the effect of the operation ; but this is very far from being the only factor. 
These remarks apply to gonocalyces in general. It must now be observed, however, 
that these remarks do not apply in equal degrees to all the genera of the covered-eyed 
Medusse which I have examined. ' In other words, if a number of individuals in each 
of several genera be subjected to the operation we are considering and the results 
tabulated, it will be found that the average degree of paralysis manifested by the 
individuals of the different genera is not uniform. For the sake of brevity, therefore, 
I shall choose a species belonging to each of the two genera which, within my limited 
experience, have shown the greatest differences in this respect ; and by giving a some- 
what detailed account of the manner in which the individuals composing these species 
behave under the form of mutilation described, I shall hope to convey a general idea 
of the manner in which individuals composing all the other species I have examined 
behave under similar circumstances — it being understood that all the other species I 
have examined occupy, in the particulars we are concerned with, a position somewhere 
intermediate between the two extremes which are described. 
The species, then, to which I allude are Aurelia aurita and Cyancea capillata, both 
exceedingly common forms. Of these species the first approaches nearest to the 
naked-eyed Medusae in the concentration of its locomotor centres into the margin of 
the swimming-organ, while the second departs most widely from the naked-eyed 
Medusse in this respect. It must be carefully noted, however, that in the case of these 
species, as well as in that of all the other species of covered-eyed Medusse I have 
examined, the individual variations in these particulars are very great. Therefore, 
while describing these individual variations in the cases of Aurelia aurita and Cyancea 
capillata, I wish it to be understood that the same remarks apply to all the species of 
the covered-eyed Medusse which I have observed. 
Excision of the entire margin of Aurelia aurita , inclusive of course of lithocysts, 
causes, in the great majority of cases, instantaneous and complete paralysis of the 
entire gonocalyx. In the minority of cases one or more supernumerary locomotor 
centres assert their presence in some part or parts of the general contractile tissue of 
the gonocalyx immediately after removal of its margin. The first of these two divi- 
sions admits of being again divided into two subdivisions. In the cases composing 
one of these subdivisions (and these are much the more numerous) additional centres 
of spontaneity become, so to speak, developed after the lapse of a greater or less 
