MR. G-. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUSAS. 
279 
while such is very rarely the case with any other portions of the marginal tissue 
when excised. 
As the question concerning the presence of a nervous system in Medusee has long 
been a warmly disputed one, it may perhaps facilitate its solution if I here observe that 
there is certainly no case in the whole animal kingdom where there is so great a dis- 
proportion between the mass of a ganglionic centre and that of the system which it is 
capable of setting in motion, as there is between the mass of a lithocyst and that of the 
gonocalyx which it animates. Thus, in order to obtain the exact proportions in the 
case of a medium-sized covered-eyed Medusid, weighing thirty pounds, I first removed 
seven of the lithocysts, and then observed that the eighth one continued to supply 
contractile impulses to the entire gonocalyx. I next cut out this lithocyst also, and 
having cleared it as much as possible of the adherent gelatinous tissue, weighed it. 
Observing further that the mutilated gonocalyx did not move for an hour after the 
operation (although previous to the operation it had been in active motion), I weighed 
this also, and obtained the surprising result, that the lithocyst had previously been 
animating a structure more than thirty million times its own weight!* 
§ 5. Summary of Division II . — With a single exception to hundreds of observations 
upon six widely divergent genera of naked-eyed Medusae, I find it to be uniformly true 
that removal of the extreme periphery of the animal causes instantaneous, complete, 
and permanent paralysis of the locomotor system. In the genus Sarsia my observations 
point very decidedly to the conclusion that the principal locomotor centres are the eye- 
specks, but that, nevertheless, every microscopical portion of the intertentacular spaces 
of the margin is likewise endowed with the property of originating locomotor impulses. 
In the covered-eyed division of the Medusae I find that the principal seat of sponta- 
neity is the margin, but that the latter is not, as in the naked-eyed Medusae, the 
exclusive seat of spontaneity. Although in the vast majority of cases I have found 
that excision of the margin impairs or destroys the spontaneity of the animal for a 
time, I have also found that the paralysis so produced is very seldom of a permanent 
nature. After a variable period occasional contractions are usually given, or in some 
cases the contractions may be resumed with but little apparent detriment. Considerable 
differences, however, in these respects are manifested by different species, and also by 
different individuals of the same species. Hence, in comparing the covered-eyed group 
as a whole with the naked-eyed group as a whole, so far as my observations extend I 
should say that the former resembles the latter in that its representatives usually have 
their main supply of locomotor centres situated in their margins, but that it differs 
from the latter in that its representatives usually have a greater or less supply of their 
locomotor centres scattered through the general contractile tissue of their swimming- 
* This individual belonged to the species Chrysaora hysoscella. From analogy, however, I doubt not that 
if I had left the animal over night, next morning it would have exhibited feeble signs of spontaneity ; for, as 
already observed, I have found it a rare thing to obtain thorough and permanent paralysis in any species 
of the covered-eyed Medusse by the excision of lithocysts. 
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