CHAPTER III. 
EXPERIMENTS IN STIMULATION. 
Mechanical, Chemical, and Thermal Stimulation. 
So far as my observations extend, I find that all 
Meduse, after removal of their locomotor centres, 
invariably respond to every kind of stimulation. 
To take the case of Sarsia as a type, nothing can 
possibly be more definite than is the single sharp 
contraction of the mutilated nectocalyx in response 
to every nip with the forceps. The contraction is 
precisely similar to the ordinary ones that are per- 
formed by the unmutilated animal; so that by 
repeating the stimulus a number of times, the 
nectocalyx, with its centres of spontaneity removed, 
may be made to progress by a succession of con- 
tractions round and round the vessel in which it is 
contained, just as a frog, with its cerebral hemi- 
spheres removed, may be made to hop along the 
table in response to a succession of stimulations.* 
* In the case of the covered-eyed Medusz, however, the 
paralyzed umbrella sometimes responds to a single stimulation 
with two, and more rarely with three contractions, which are 
separated from one another by an interval of the same duration 
as the normal diastole of the unmutilated animal. 
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