74 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
But, lastly, the strongest evidence in favour of 
this view as afforded by the following observations. 
At the beginning of this treatise I stated that the 
distinguishing function of nerve consists in its power 
of conducting stimuli to a distance, irrespective of 
the passage of a contraction-wave ; and I may here 
add that when a stimulus so conducted reaches a 
ganglion, or nerve-centre, it causes the ganglion to 
discharge by so-called “reflex action.” Now, this 
distinguishing function of nerve can plainly be 
proved to be present in the Medusze. For instance, 
take such a section of Aurelia as this one (Fig. 12), 
that the propagation of the wave is at least in some measure 
dependent on nervous conduction. This fact is, that after a 
contraction-wave has been blocked by the severity of a spiral or 
other form of section, it may again be made to force a passage 
under the influence of vagus stimulation. 
Moreover, in a paper still more recently published by Drs. Brunton 
and Cash on “ Electrical Stimulation of the Frog’s Heart” (Proc. 
Roy. Suc., vol. xxxv., No. 227, p. 455, et seg.) it is remarked, 
** Another interesting consideration is, whether the stimulus which 
each cavity of the heart transmits to the succeeding one consists 
in the propagation of an actual muscular wave, or in the 
propagation of an impulse along the nerves. The observations 
of Gaskell have given very great importance to the muscular 
wave occurring in each cavity of the heart of cold-biooded animals 
as a stimulus to the contraction of the next succeeding cavity. 
Our observations appear to us to show that, while this is an 
important factor, it is not the only one in the transmission of 
stimuli. . . . We consider that stimuli are also propagated from 
one chamber of the heart to another through nervous channels: 
thus we find that irritation of the venus sinus will sometimes 
produce simultaneous contractions of the auricle and ventricle, 
instead of the ventricular beat succeeding the auricular in the 
ordinary way. This we think is hardly consistent with the hypo- 
thesis, that a stimulus consists of the propagation of a muscular 
wave only from the auricle to the ventricle.” 
