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ME. Gf. J. EOMANES ON THE LOCOMOTOE SYSTEM OE MEDTJSiE. 
to lay most stress upon the first one ; for he merely mentions the second method in a 
short footnote towards the end of his paper, and there states that he only tried it in 
a few cases. Yet to me it seems that for the object in view the second method is much 
more trustworthy than the first. I am well aware of the fact, pointed out by Dr. 
Eimer, that upon each contraction of a given segment of Aurelia aurita the two arms 
of the so-called “contractile zone” approximate each other, and that this gives rise 
to the appearance of spontaneous action on their part. I think, however, that this 
appearance is deceptive, being caused only by the absence of resistance at the inter- 
rupted part of the margin to the pressure exerted by the contraction of the immediately 
surrounding tissues. At any rate, so long as this possible explanation has not been 
thoroughly excluded by experiments conducted on the converse method of removing 
the lithocysts from between the arms of the contractile zone, so long, it seems to me, 
must the method we are considering be valueless. The question, then, must be decided 
by the converse method just alluded to, and by it alone. Now I have made experiments 
according to this method, and, so far as I remember, in every case, when sufficient care 
was taken to remove all the lithocysts, the contractile zone entirely ceased its contrac- 
tions. And not only so, but by removing, with the aid of a well-pointed scissors, the 
little sac of crystals composing the central part of the lithocyst, without injuring the 
curious wing-like appendages by which this sac is partly surrounded, and, conversely, 
by removing in other specimens these wing-like appendages alone, without injuring the 
little sac of crystals — by these experiments I was able to satisfy myself that the whole 
spontaneity of the lithocyst appeared to be exclusively lodged in the minute sac of 
crystals referred to. 
There is thus in this particular a direct contradiction between the results of Dr. 
Eimer’s experiments and those of my own. I should therefore like to state that my 
experiments with reference to this subject were not made till near the end of the 
season, and so at a time when the only specimens I could procure were small and not 
very active. In view of this fact I intended to defer publishing any account of the 
experiments now detailed until I had an opportunity of confirming them on vigorous 
specimens ; but a perusal of Dr. Eimer’s statements appears to render it desirable for 
me to give an opinion now upon the point under consideration, although I confess 
that, for the reason just mentioned, I do so with some diffidence. 
I fully agree with Dr. Eimer in his view that the contractions of Aurelia aurita are 
“ usually involuntary,” but that they are nevertheless to a certain extent subject to 
the control of volition. As stated in the beginning of this paper, I believe that 
different species of Medusae are endowed in different degrees with the power of 
volition ; and in this respect I should place Aurelia aurita at the head of all the covered- 
eyed species I have observed : its contractions are not of so purely rhythmical a nature 
as are those of Cyanoea cajpillata , &c. 
But this leads us to the next observation mentioned by Dr. Eimer, viz. that the 
length of the pauses between any series of contractions bears a direct relation to the 
