41 6 G. H. Parker. 



taining whether waves passed beyond it. When a plate in Beroe 

 is turned aborally by a lancet point, waves from the aboral end 

 fail to pass this plate. If only the tip of the plate is held and the 

 base is allowed to move, the wave passes onward to the oral portion 

 of the row. These observations led Verworn ('90, p. 171) to 

 conclude that the mechanical vibrations of the plates were neces- 

 sary for transmission, and he drew this conclusion notwithstanding 

 the fact that in Cestus he ('90, p. 172) found that the holding or 

 even the pulling out of a plate did not interfere with transmission. 

 Verworn confessed to have been astonished at the conditions 

 found in this species, but, as already stated, he believed that they 

 might be explained on the assumption that the base of each plate 

 is more or less surrounded by cilia which after the removal of the 

 plate continue to transmit mechanically. Unfortunately I have 

 been unable to try the experiment of restraining plates in Mnem- 

 iopsis, for the rows of plates in this species, like those in Beroe, as 

 pointed out by Krukenberg ('80, p. 10), are so sensitive to mechani- 

 cal stimulation that the moment they are touched they are drawn 

 down into the animal's body to such an extent as to make experi- 

 ments of this kind very unsatisfactory, if not impossible. 



Although the great sensitiveness of the rows of plates in Mnem- 

 iopsis prevented me from trying the experiment of holding plates 

 individually, it afforded a very natural means of checking their 

 action. As Verworn ('90, p. 170) has shown, when the middle of 

 a row of plates is touched, the row in that region becomes depressed 

 and the edges of the depression fold over and cover the plates. 

 Thus in Mnemiopsis half a dozen plates may become so much 

 restrained that they will not show the least motion and yet waves 

 that arrive at the aboral entrance to this depression emerge from 

 its oral end with the greatest regularity. This may happen while 

 the covered region is under close inspection through a lens and 

 gives not the least sign of plate or ciliary movement. I am, 

 therefore, forced to conclude, that, contrary to the statement made 

 by Verw^orn ('90, p, i/o), such restrained tracts transmit with 

 perfect regularity even in the absence of observable ciliary and 

 plate motion. 



Kraft ('90, p. 223) in his study of the ciliated epithelia of verte- 

 brates, showed that, though low temperature may bring cilia to a 

 standstill, it does not greatly check the transmitting power of the 

 tissue. It ought, therefore, to be possible to check the action of 



