32  JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
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 marginal bodies and leaving the latter 
untouched, is not so definite as is the effect of the 
cohverse experiment 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 impos- 
sible to decide how much of the enfeebling effect of 
the section is due to the removal of locomotor 
centres from the swimming-bell, 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 marginal bodies 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 case of this genus, to animate 
the entire swimming-bell. Choosing vigorous 
* See Fig. 1. 
