CHArXER III. 



EXPERIMENTS IN STIMULATION. 



Mechanical, Chemical, and Thermal Stim^ulation. 



So far as m}^ observations extend, I find that all 

 Medusre, 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 t^e 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 Medusas, however, the 

 paralyzed Timbrella sometimes responds to a single stimtilation 

 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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