278 
MR. Gr. J. ROMANES ON THE LOCOMOTOR SYSTEM OE MEDUS2E. 
either by excising the lithocysts alone or by leaving the lithocysts in situ and excising 
all the rest of the marginal tissue, I have ever detected the slightest indications of 
locomotor centres being present in any part of the margin of the gonocalyx other than 
the eight lithocysts ; so that all the remarks made upon this species in § 2, while we 
were dealing with the effects of excising the entire margin of gonocalyces, are equally 
applicable to the experiment we are now considering, viz. that of excising the litho- 
cysts alone. In other words, but for the sake of symmetry I might as well have 
stated at the first, that in the case of Aurelia aurita all the remarkable paralyzing 
effects which are obtained by excising the entire margin of a gonocalyx are ob- 
tained in exactly the same degree by excising the eight lithocysts alone : the inter- 
mediate marginal tissue, in the case of this species, is totally destitute of locomotor 
centres. 
I have in this section chosen Aurelia aurita as the type of the covered-eyed Medusse, 
because, from the flattened shape of its gonocalyx, the differential experiment of cutting 
out lithocysts and intermediate marginal tissue respectively admits of being conducted 
in a fairer way than in the case of any other species of the group I have happened to 
come across ; for, in the case of these other species, the form of the gonocalyces 
necessitated excision of large masses of contractile substance before all the tissue 
included between the lithocysts could be wholly removed. It therefore became impos- 
sible for me in these cases to determine how much of the paralyzing effect was due to 
removal of locomotor centres, and how much to possibly general shock. But although 
I was thus precluded from making any trustworthy experiments upon the effect of 
cutting out all the marginal tissue from between the lithocysts of these species, I was 
of course able to perform the converse experiment of cutting out the lithocysts alone. 
The result of numerous experiments of this kind is to satisfy me that, in all the 
species of covered-eyed Medusae I have examined, the chief marginal supply of loco- 
motor centres is aggregated in the eight lithocysts, although I am unable, for the 
reasons just given, to say whether or not the exclusive marginal supply of these 
centres is so aggregated. From this it will readily be gathered that, in all the species 
of covered-eyed Medusae I have examined, the paralyzing effects of excising the 
lithocysts alone are most strongly marked, although, of course, from what has been 
said upon this group in § 2, it will be understood that the experimenter must be 
prepared to meet with all grades of individual variations in this respect. With regard 
to specific differences, it will now be apparent that Aurelia [aurita is, of all the forms 
I have examined, the one that is most strongly affected by removal of its lithocysts, 
the paralysis of the gonocalyx thus caused being, in some cases, as permanent as it 
is total. In all the other species of covered-eyed Medusse examined, I have found it 
a very rare thing to obtain permanent paralysis by excision of lithocysts. It may here 
be added that a portion of any size of contractile tissue left adhering to an excised 
lithocyst of any species of covered-eyed Medusa will very frequently be found to 
continue its rhythmical contractions after its severance from the main organism, 
