ME. G. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUSiE. 
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marginal bodies without injuring the rest of the margin, and vice versa. The results 
of such experiments upon members of this genus are as follow. 
Whatever be the condition of the individual operated upon as to freshness, vigour, 
&c., it endures excision of three of its eye-specks without suffering any apparent 
detriment; but in most cases, as soon as the last eye-speck is cut out, the animal 
falls to the bottom of the water quite motionless. If the subject of the experi- 
ment happens to be a "weakly specimen it will perhaps never move again : it 
has been killed by something very much resembling nervous shock. On the other 
hand, if the specimen operated upon be one which is in a fresh and vigorous state, 
its period of quiescence will probably be but short ; the nervous shock (if we may so 
term it), although evidently considerable at the time, soon passes away, and the animal 
resumes its motions as before. In the great majority of cases, however, the activity 
of these motions is conspicuously diminished. 
The effect of excising all the marginal tissue from between the eye-specks and 
leaving the latter untouched is not so definite as is the effect of the converse experi- 
ment just described. Moreover allowance must here be made for the fact that in this 
experiment the principal portion of the “ veil ” is of necessity removed ; so that it 
becomes impossible to decide how much of the enfeebling effect of the section is due 
to the removal of locomotor centres from the nectocalyx, and how much to a change 
in the merely mechanical conditions of the organ. From the fact, however, that 
excision of the entire margin of Sarsia produces total paralysis, while excision of the 
eye-specks alone produces merely partial paralysis, there can be no doubt that both 
causes are combined. Indeed it has been a matter of the greatest surprise to me 
how very minute a portion of the intertentacular marginal tissue is sufficient, in the 
case of this genus, to animate the entire nectocalyx. Choosing vigorous specimens of 
Sarsia, I have tried, by cutting out all the margin besides, to ascertain how minute a 
portion of intertentacular tissue is sufficient to perform this function, and I find that 
this portion may be so small as to be quite invisible without the aid of a powerful 
lens. As it not unfrequently happens that in cutting out the extreme margin of 
Sarsia a minute part of the intertentacular tissue is left behind accidentally, I may here 
caution any one who repeats the fundamental observation upon this genus to be very 
careful in removing every atom of the marginal canal. 
From numerous observations, then, upon Sarsia, I conclude that in this genus 
(and so, from analogy, probably in all the other genera of the true Medusae) loco- 
motor centres are situated in every part of the extreme margin of a nectocalyx, 
but that there is a greater supply of such centres in the marginal bodies than 
elsewhere. 
§ 4. Effects of excising certain portions of the margins of Gonocalyces. — Coming now 
to the covered-eyed Medusae, I find that the concentration of the locomotor centres of 
the margin into the marginal bodies, or lithocysts, is still more decided than it is in 
the case of Sarsia. Taking Aurelia aurita as a type of the group, I cannot say that, 
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