ME. Gr. J. EOMANES ON THE LOCOMOTOE SYSTEM OF MEDUSAE. 
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( (vii) Both electrodes in the pigment part of an eye-speck. Bell first contracted 
| at 8 centims. 
j (viii) Both electrodes in the vesicular part of an eye-speck. Bell first contracted 
l at 12 centims. 
With regard to the other parts of the nectocalyx, I have merely to state that there 
is a marked difference between the excitability of this organ when the electrodes are 
placed upon any one of the four radiating canals (and so upon the ascending nerve- 
chains described by Agassiz) and when the electrodes are placed upon the tissue 
between any of the canals. The ratio is generally about 9 centims. : 6-g- centims. 
Thinking that this greater excitability of the bell when the electrodes were placed 
upon one of the radiating canals than when they were placed upon the intermediate 
tissue might possibly have been due to a slight escape of electricity, which in the one 
case would have become diffused over the muscular tissue of the bell, while in the 
other it might have been conducted to the marginal centres by a possibly high con- 
ducting-power of the radiating canal, I took the precaution of removing the margin 
altogether ; but this did not modify the results. 
I conclude, therefore, that in almost every particular there is, in the case of Sarsia, 
a perfect coincidence between the microscopical observations of Prof. L. Agassiz and 
the results yielded by the method of exploration by stimulus just described. Never- 
theless I may here repeat what I said in the opening section, viz. that the inference so 
confidently drawn by that observer as to the function of the histological element he 
described was, as an inference, decidedly premature*. 
(C) I must now describe a mode of section which would naturally fall under the 
next division of my subject, were it not for its great value in enabling us to conduct an 
important part of the inquiry relating to electrical stimulation. 
* It is worth while to observe also, as showing the danger of drawing conclusions concerning function from 
histological observation alone, that although Prof. Agassiz was so positive regarding the localization of nervous 
tissue in the margins of Medusae, he had no idea that the function of this supposed nervous tissue was so 
intensely specialized, — witness the passage already quoted, “ There is unquestionably a nervous system in 
Medusae, hut this nervous system does not form large central masses to which all the activity of the body is 
referred, or from which it emanates.” 
There is another remark which may here he made. Prof. Agassiz somewhere observes that it is noteworthy 
how, in the naked-eyed Medusae, the supposed nervous tracts follow everywhere the course of the nutritive 
system. Now, as my method of exploration by stimulus has yielded results confirmatory of Prof. Agassiz’s 
views in this respect, it becomes worth while to speculate as to whether the greater diffusion of the centres of 
spontaneity in the covered-eyed than in the naked-eyed group of Medusae may not stand in some relation to 
the characteristically greater diffusion of the nutritive system in the one group than in the other. Certain it 
is that lithocysts always appear to stand in some peculiar anatomical relation to the nutritive canals, the latter 
sweeping round to meet the former (see Plate 32) and communicating through them with the external water. 
This, of course, may only be due, as Gegenbaue supposes, to the lithocysts having some excretory function to 
perform ; hut now that these organs have been raised to the dignity of locomotor centres, and analogous centres 
have been proved to he similarly associated with nutritive tracts in the naked-eyed Medusae, it is well to 
remember, in view of some deductions from the general theory of evolution, that this possibly non-accidental 
association of nutritive systems with the earliest indications of nervous systems may turn out to be an associa- 
tion of no small significance. 
