80 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 



continuity — it thus becomes a possibility that in 

 these cases no such anatomical continuity exists, 

 but that the pliysiological continuity is maintained 

 by some such process of physiological induction as 

 probably takes place among the nerve-fibres of 

 Aurelia.* 



I have now to detail another fact of a very 

 puzzling nature, but one which is certainly of 

 importance. When the spiral section is performed 

 on Aurelia auvita, and when, as a consequence, the 

 contraction-waves which traverse the elongating 

 strip become at some point suddenly blocked, if the 

 section be stopped at this point it not unfrequently 

 happens that after a time the blocking suddenly 

 ceases, the contraction -waves again passing from 

 the strip into the umbrella as freely as they did 

 before the section reached the point at which the 

 blocking occurred. The time required for this 

 restoration of physiological continuity is very 

 variable, the limits being from a few seconds to an 

 hour or more ; usually, however, it is from two 

 to four minutes. This process of i e-establishing 

 the physiological connections, although rapid, is 

 not so instantaneous as is that of their destruction 

 by section. In general it requires the passage of 

 several contraction- waves before the barrier to the 

 passage of succeeding waves is completely thrown 



* That it can scarcely be electrical induction would seem to be 

 shown by the fact that such effects can only be produced on 

 nerves by strong currents, and also by the fact that the saline 

 tissuesof the swimming.bell must sTiort-circuit any feeble electncal 

 currents as soon as they are genoratnd. 



