MR. G. J. ROMANES ON THE LOCOMOTOR SYSTEM OE MEDUSAS. 
665 
II. RHYTHM. 
§ 1. Relation between Size and Rhythm. — It will be convenient here to introduce all 
the observations that I have been able to make with regard to the natural rhythm of 
the Medusae. As Dr. Eimer has also made some observations in this connexion, before 
proceeding with the fresh points having relation to this subject, I shall consider those 
points to which allusion was made in my Postscript. 
In Aurelia aurita , as Dr. Eimer has noticed, the rate of the rhythm has a tendency to 
bear an inverse proportion to the size of the individual. Size, however, is far from 
being the only factor in determining the differences between the rate of the rhythm 
of different specimens — the individual variations in this respect being very great even 
among specimens of the same size. What the other factors in question may be, how- 
ever, I am unable to suggest. 
§ 2. Relations between the periods of Activity and the periods of Repose. — Dr. Eimer 
affirms that the duration of the natural pauses, which in Aurelia sometimes alternate 
with bouts of swimming, bears a direct proportion to the number and strength of the 
contractions that occurred in the previous bout of swimming. In my Postscript I 
observed that Sarsia are much better adapted than Aurelia for determining whether 
any such precise relation obtains ; for, in the first place, the strength of the con- 
tractions is more uniform, and, in the next place, the alternation of pauses with 
bouts of swimming is of a more decided character in Sarsia than in healthy 
specimens of Aurelia. 1 further observed that in Sarsia I was quite sure no such pre- 
cise relation did obtain, although in a very general way it was true, as might be 
expected, that unusually prolonged bouts of swimming were sometimes followed by 
pauses of unusual duration. At that time I had not taken the trouble actually to 
count the pulsations and to time the intervals of rest, and so could not say any thing 
more upon the subject. This year, however, I have made precise observations with 
regard to this matter, and I find that they fully confirm my previous statements. As 
all the observations are very much the same, I shall only quote two of them : — 
Schafer’s work, two other monographs have appeared on the histology of the nervous tissues of the Medusas. 
One of these monographs is by Messrs. Hertwig, and the other by Prof. Eimer. In my next paper I shall give 
an abstract of both, and shall therefore not burden this Postscript by endeavouring to do so at present. But 
I should like to take this the earliest opportunity of rectifying an injustice which, as I now learn from Prof. 
Eimer’s last paper, I previously did him in my first paper. In my Postscript to that paper I stated that in our 
independent observations concerning the effect of excising lithocysts I had a right to claim priority, both as 
regards observation and publication. Prof. Eimer, however, now explains that, in consequence of his first paper 
having been hound in the Wiirtzburg Yerhandlungen without its proper titlepage, the reference to the date of 
his work which occurs in the paper itself (“ d. J.”) refers, not to the year on the back of the volume, hut to the 
year preceding. Therefore, although I was right in saying that I had anticipated Dr. Eimer in making the “ fun- 
damental observation,” I was wrong in supposing that I had also anticipated him in publishing this observa- 
tion. Dr. Eimer has thus a full right to claim priority as regards this and all his other researches concerning 
the nervous system of Medusae. — 1878.] 
