The Movements of the Sivimming-Plates in Ctenophores. 413 



ing to Krukenberg ('80, p. 2) and Verworn ('90, p. 156), the activ- 

 ity of the oral part may not return for an hour or so after the row 

 is cut. The waves in the oral part of Mnemiopsis always proceed 

 from near the cut end of the row orally; the most aboral plate to 

 show motion, however, is not the one next the wound but usually 

 the third or fourth from it. The oral portion will thus move its 

 swimming-plates for hours without relation to the movements of the 

 aboral part. I have never seen any evidence of the reestablishment 

 of harmony in the two parts of a severed row such as has been 

 described by Eimer ('80, p. 229) and Verworn ('90, p. 167; '91, 

 p. 463). When a swimming-plate band is cut through, not where 

 there are swimming-plates but between the most aboral plate and 

 the sense body (compare Fig. 2), the whole row in its movements 

 becomes independent of the sense body and if the sense body is 

 destroyed, the coordination of the four pairs of rows entirely 

 disappears, as has already been shown by Verworn ('91, pp. 

 457-459) and others for several European species. 



When a Mnemiopsis is cut in two transversely, the parts of rows 

 on the aboral portion retain their coordination as in a normal 

 animal; those on the oral part, as might be expected, lose all signs 

 of such relations. It is clear from this and the preceding experi- 

 ments that the coordinating influences proceed from the aboral 

 pole, and, when this is lost, coordination disappears. In this 

 respect my observations confirm those of Krukenberg ('80, p. 2) 

 on Beroe and are opposed to those of Eimer ('80, p. 231), who 

 stated that the oral half of Beroe is indistinguishable in the move- 

 ments of its plates from a whole animal. 



When a Mnemiopsis is shaken in sea-water, it can be broken 

 easily into fragments and the plates attached to these pieces will 

 continue to beat rhythmically and metachronally for from one to 

 two days. As Verworn ('90, p. 157) has shown for Cestus, so 

 also in Mnemiopsis, even a single plate with a small basal piece of 

 protoplasm will beat rhythmically for a long time. This condi- 

 tion led Verworn to believe that each plate possessed a certain 

 degree of autonomy, which was seen in the continued activity of 

 the isolated plates atid must be imagined to be counteracted 

 by some influence when the plate as a member of a row was 

 quiescent. But in my opinion the swimming-plate, when it beats, 

 does so because it is stimulated, and its quiescence is evidence of 

 the absence of appropriate stimuli. When it beats normally on 



