308 
ME. a. J. EOMANES ON THE LOCOMOTOE SYSTEM OE MEDUSAS. 
a tendency to assume a bell-shape. In consequence of this slight change of form, the 
two halves were now able to swim at all level's in the water, and were no longer 
obliged, as on the previous day, to lie at the bottom of the vessel. In spite of every 
care these two halves died on the third day, presumably from the want of food. 
By counting the rate of the pulsations in entire animals, and then dividing these 
animals by radial incisions into halves, quarters, or eighths, in such a manner that each 
portion should contain at least one lithocyst, and, lastly, by counting the rate of the 
pulsations of the halves, quarters, or eighths, Dr. Eimer was able to satisfy himself 
as to the following very important fact : — The sum of the contractions performed 
by all the parts of a divided animal was, in a given time, equal to the number of 
contractions which had been performed by that animal before its mutilation. This 
rule, however, was liable to very frequent variations. 
Portions thus severed and kept without nourishment manifest after a time a progres- 
sive retardation in the rate of their contractions. Want of fresh sea-water also has the 
same effect, producing the greatest irregularity in the rate, strength, and rhythm of the 
pulsations. Addition of fresh sea- water revives the animal even from a state of ap- 
parent death, when the contractions return to their normal strength and rhythm. 
Dr. Eimer also made the following experiments in section. From the margin of 
Aurelia anrita he carried a radial incision of several millims. long, in order to test a view 
which he attributes to Haeckel, viz. that all the nervous connexions in Medusae are 
dependent upon a single peripheral ring. Of course he obtained negative results, and 
thereupon lengthened his radial section until it came within 8 millims., and in another 
individual within 6-§- millims. from the ovarian pouch. He then found that at this point 
the two portions of the animal first became physiologically separated. 
Next, in order to test Agassiz’s view as to the presence of an upper nervous ring and 
the possibility in the former experiments of this ring having acted vicariously for the 
divided portion of the lower ring, Dr. Eimer made two radial incisions proceeding 
from the centre towards the circumference of the disk. He found, of course, that these 
sections might be carried to within quite a short distance of the margin before the 
portion of tissue which was included between them became physiologically separated 
from the rest of the umbrella. 
Lastly, as a control experiment, the author cut out from the middle of an Aurelia 
measuring 10 centims. in diameter a circular mass measuring centims. in diameter, 
thus reducing the margin of the animal to the form of an open ring. This marginal 
ring continued, of course, to contract, and this at first more rapidly than usual. On 
the other hand, all spontaneity ceased in the other part of the animal after an interval 
of three hours. Dr. Eimer then submitted this open ring to a series of interdigi- 
tating cuts. He found that in no one of its parts was the physiological continuity of 
the tissue destroyed by the sections, although it seemed to him that the severer forms 
of such section tended partially to obstruct the passage of the contractile influence 
from one division to another— -that the thinner the connecting link of tissue, the 
