MR. Or. J. ROMANES ON THE LOCOMOTOR SYSTEM OE MEDUSiE. 
751 
case with any other substance which 1 have tried. Brine acts as an anaesthetic, and, in 
depriving the tentacles and polypite of their muscular tonus, exerts an effect the oppo- 
site of that which is exerted by fresh water. 
Postscript. 
Having been in private correspondence with Prof. Eimer during the time that this 
paper was passing through the press, I now (April 9th, 1878) learn from him that all the 
differences which have hitherto existed between our statements admit of being recon- 
ciled. At his request, therefore, and in order to explain the character of the recon- 
ciliation, I append this Postscript. 
The points wherein Prof. Eimer’s observations did not perfectly agree with mine, or 
mine with his, were three in number : — 
1st. We were not at one regarding the alleged rule that when an Aurelia is 
artificially segmented the rate of the rhythm which is manifested by each of the 
segments severally bears a direct proportion to the size of the segment, and this in a 
ratio such that the sum of the contractions which are performed by all the severed 
segments in a given interval of time is equal to the number of contractions which the 
unmutilated organism had previously performed in a similar interval of time. Dr. 
Eimer explains that further observation on his part has not tended to confirm this 
rule, and therefore that he desires his previous statements on this subject to be 
considered as withdrawn. 
2nd. With regard to the character of the “ secondary contractions ” which always 
supervene in the covered-eyed Medusse after removal of their lithocysts, our results 
have not hitherto been in full agreement. Dr. Eimer has described these contractions 
as irregular, inefficient, and feeble contractions, which are of a local nature and rarely 
last any considerable time after removal of the lithocysts — generally ceasing after a few 
moments, or, at any rate, after several hours. On none of these points did my obser- 
vations altogether harmonize with this description, and I am therefore most glad to 
learn from Dr. Eimer that his further observations have now brought his views on all 
these points into precise agreement with my own. 
3rd. Lastly, the difference of opinion which existed between us with regard to the 
exact seat of spontaneity in the covered-eyed Medusae has also been happily removed. 
It appears that I have hitherto been under some misapprehension as to the precise area 
of tissue which Dr. Eimer intended to denote by his term “ contractile zone for 
while I have hitherto supposed that by the term “ contractile zone ” Dr. Eimer intended 
to denote “ the crescent-shaped interruption of the margin in which the lithocyst, 
together with its gelatinous hood, is situated”*, I now learn that I was incorrect in this 
supposition. From Prof. Eimer’s letter I do not quite recognize the precise tissue-area 
which he endeavours to describe as the area to which his term “ contractile zone ” is 
* Quoted from the Postscript to my Croonian Lecture, 1876, Phil. Trans, p. 309. 
MDCCCLXXVII. 5 N 
