132 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
perhaps, still further increased by the result of the 
following experiments. 
If a covered-eyed Medusa be chosen in which 
perfectly synchronous action of the ganglia is 
observable, and if a deep radial incision be made 
between each pair of adjacent ganglia—the incisions 
being thus eight in number and carried either from 
the margin towards the centre or vice versd—it 
then becomes conspicuous enough that the eight 
partially divided segments no longer present syn- 
chronous action; for now one segment and now 
another takes the initiative in starting a contraction- 
wave, which is then propagated to the other 
segments. And it is evident that this fact tends to 
negative the above explanation, for if the discharges 
of the ganglia are independently simultaneous 
before section, we might expect them to continue so 
after section. It must be remembered, however, 
that the form of section we are considering 1s a 
severe one, and that it must therefore not only give 
rise to general shock, but also greatly interfere with 
the passage of contraction-waves, and, in general, 
disturb the delicate conditions on which, according 
to the suggested explanation, the previous harmony 
depended. Besides, as we shall subsequently see, 
for some reason or other segmentation of a Medusa 
profoundly modifies the rate of its rhythm. In 
view of these considerations, therefore, the results 
yielded by such experiments must not be regarded 
as having any conclusive bearing on the question 
before us; and as these or similar objections 
apply to various other modes of section by which 
