ME. Gr. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUSiE. 
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usually very long, though different individuals manifest considerable difference in this 
respect, in some cases a great many more contractions occurring in a given time than 
in other cases. It is not unfrequently observable that these after-contractions occur in 
pairs, and more rarely in triplets ; and when this is the case the interval of diastole 
corresponds with that which occurs in ordinary swimming. 
So much for the rhythmical nature of these after-contractions of Aurelia aurita. 
With regard to their other qualities, I have nothing further to add. I am still unable 
to say that they appear to me either more “ inefficient ” or more “ feeble ” than the 
contractions which proceed from a single remaining lithocyst of average potency, 
particularly if the comparison be made between the former and the latter after a pause 
of a minute or more has in each case intervened between the contractions observed and 
the previous contraction (see III. (A) (a)). I have also been unable to perceive that the 
secondary contractions are any more of a “local” nature than are the primary ones. 
In almost every instance which I have this year observed, the description just quoted 
from my Postscript was strictly applicable ; and those comparatively few instances in 
which the secondary contractions were local, were not much, if at all, more numerous 
than those in which primary contractions proceeding from a single remaining lithocyst 
were local. Again, my experience has this year been quite at variance with that of 
Dr. Eimer as regards the time after removal of the lithocysts during which the secon- 
dary movements persist. Numerous experiments have shown that it certainly is not 
correct to say that these contractions “ generally cease after a few moments,” or even 
“ after several hours.” Indeed so far have I found it from being true that they “ rarely 
last any considerable time,” that I am now able fully to confirm my original “ impres- 
sion,” and to state positively that these after-contractions of Aurelia aurita “ usually 
last for several days.” For in some dozens of experiments I have found no exception 
to the rule that, if an ordinarily fair chance be given to the mutilated animals by 
keeping them in a basin-shaped vessel at a temperature not greatly above that of the 
sea and changing the water once a day, these secondary contractions persist for one day 
at the least, generally for two or three days, and sometimes longer. In most cases they 
continue after decomposition of some parts of the tissues has set in, and even after such 
decomposition has proceeded to the extent of giving the latter a certain ragged appear- 
ance, which is due to portions disintegrating into shreds. These remarks apply to many 
cases in which, not the contractile zones merely, but the entire margin had been removed. 
Lastly, with regard to the greater vitality of unmutilated covered-eyed Medusae with 
their lithocysts in situ than those which have had these bodies removed, I have found 
my previous statement substantially correct. There are wonderful individual variations, 
however, in this respect ; for sometimes the irritability of the paralyzed specimens will 
remain after that of unmutilated specimens which are exposed to exactly the same con- 
ditions has been destroyed by decomposition. Comparisons, therefore, in this respect 
can only be fairly made between detached segments of the same individual ; and 
in this case it may be taken as a rule that the segments in which the lithocyst is 
