.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 maro-inal bodies and leavinoj the latter 

 untouched, is not so definite as is the effect of the 

 converse 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 

 oro-an. From the fact, however, that excision of the 

 entire margin of Sarsia produces total paralj^sis, 

 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 



* See Fiff. 1. 



