ME. GL J. EOMANES ON THE LOCOMOTOE SYSTEM OF MEDUSA. 
307 
previous number and strength of the pulsations. If the unmutilated animal be pricked 
with a needle, it endeavours to swim away from the source of irritation. 
If the unmutilated animal be carefully watched while performing its locomotor con- 
tractions, it will be seen that the latter emanate from the margins of the crescent-shaped 
notches, i. e. from the “ contractile zones ; ” upon every contraction the two sides of 
each zone approximate each other. Usually all the eight contractile zones contract 
together ; but this is not always the case. Frequently the contraction originates in one 
or in several neighbouring zones simultaneously, and then propagates itself with lightning 
speed to all the others, which thereupon contract either simultaneously or in rapid 
succession. Thus the animal is no doubt able to steer itself in any direction it chooses. 
From all this, then, it appears that a locomotor contraction of the umbrella may 
proceed from one, from several, or from all the zones simultaneously ; but in no case can 
a contraction of one zone take place without being accompanied by a synchronous, or 
almost synchronous, contraction of all the others. 
The number of contractions in a given time appeared to vary in an inverse proportion 
to the size of the animal. Upon excising all the contractile zones save one, the con- 
tractions were seen to emanate from this zone alone, and from thence to spread them- 
selves all over the umbrella. On now excising this last remaining zone, all contractions 
suddenly ceased. Occasionally, however, there supervened several irregular , inefficient, 
and feeble contractions, which were of a more local nature. It was rarely that these 
contractions lasted for any considerable time ; generally they ceased after a few moments, 
or at any rate after several hours : only in one case was it observed that they continued 
on the following day. 
Immediately after this operation the animal usually remains motionless, as if suffering 
from shock, and it is only after an interval that it begins to make attempts at contrac- 
tions. These attain a certain degree of vigour and then again decline. Mechanical 
stimulation, e. g. pricking the umbrella, causes in the mutilated organism responsive 
attempts at contraction ; but sooner or later, after the spontaneity of the animal has been 
destroyed by excision of the contractile zones, the irritability of the contractile tissues 
disappears, and death of the tissues supervenes. Having placed three specimens of 
Aurelia aurita under similar conditions, Dr. Eimer removed all the lithocysts from one 
of them, all save one from another, and none at all from the remaining specimen. The 
specimen which had all its lithocysts removed began to show symptoms of decomposition 
(aufgelost), while the other two specimens were still quite lively. 
Next are detailed some experiments in bisecting specimens of Aurelia aurita through 
their whole diameter. It was observed that the shock which this operation entailed 
appeared to be more severely felt by the small individuals than by the large. It was 
also observed that in one experiment the two halves contracted independently, so that 
the number of contractions which were made in a given time by the one was no 
index of the number given in the same time by the other. On the day subsequent to 
the operation, however, both halves contracted pretty uniformly, and each half showed 
