vii EXPERIMENTS ON BE ROE 357 



found active movement going on in almost all the pieces ; in 

 A, however, the plates were most active, and some of the B 

 and C pieces showed no motion. 



Then I cut off small fragments from these various portions 

 of the animals. The swimming -plates of these fragments 

 were immediately after the operation in all cases motionless, 

 but after two -hours I found active movement going on in 

 them also. 



On the second day the plates were still in active motion in 

 all the pieces, the small fragments included, excepting a few 

 of the latter. On the third day all showed active movement. 



On the piece forming the middle portion of one Beroe was 

 exhibited the peculiar phenomenon, that the plates of one row 

 vibrated in the opposite direction to that of the others, and 

 the movement in this row was no less active than elsewhere, 

 and, as in the others, proceeded in waves in rapid succession. 

 Everywhere else the movement in the separate pieces pro- 

 ceeded in the same direction in which the plates vibrated in 

 the entire animal: the waves passed from the aboral pole 

 towards the mouth. 



This reversion of direction in the swimming -plates of a 

 single row of one piece of an animal while the rest vibrated 

 normally forms a very remarkable instance of independent 

 nervous action in a separate piece of an animal, an instance 

 of reversal of function. Moreover, I observed repeatedly on 

 the separated tube-shaped middle portion of a Beroe that the 

 movement in one and the same series of plates could proceed 

 now in one direction, now in the other. 



Many repetitions of such experiments gave the same 

 results : the movement of the swimming-plates always ceased 

 after the division for a moment or for some minutes, some- 

 times even for some hours, but in all cases recommenced, 

 reappearing always earliest in the pieces which contained the 

 sense-organ, and later in the others. Usually also in the 



