The Movemejits of the Sivtmwing-Plates in Ctenophores. 415 



facts are explainable on either the theory of neuroid transmission 

 as advocated by Engelmann, or on that of mechanical transmis- 

 sion as put forward by Verworn; for on the former assumption 

 the band of epithelium leading from the sense body to the oral 

 end of a row of swimming-plates may serve as a transmitting 

 tract, and on the latter the ciliated bands leading from the sense 

 body to the rows of plates may serve to transmit the mechanical 

 disturbance from the center to the plates. I propose now to turn 

 to certain observations that are, in my opinion, inconsistent with 

 one or other of these theories. 



Since in accordance with the idea of mechanical transmission 

 the mechanical activity of the vibratile elements is a necessary 

 accompaniment of transmission, it follows that any means of 

 bringing this activity to a standstill ought to check transmission. 

 It might be supposed that the cutting off of one or more plates 

 would produce such an effect. When this is done in Cestus, 

 according to Verworn ('90, p. 173), and in Mnemiops:s, according 

 to my own observations, the waves still pass regularly over the 

 whole row of plates and are not interrupted by the interval from 

 which the plates have been removed. Since, however, the spaces 

 between the plates in Cestus, as well as in the lobate ctenophores, 

 have been shov/n by Samassa ('92, p. 229) to be ciliated, it might 

 be assumed that these cilia in their vibrations transmit the 

 mechanical disturbance over the whole row. The assumption that 

 in the absence of plates the cilia may transmit the disturbance is, 

 however, in my opinion improbable, for the space made by the 

 removal of a plate is so considerable in comparison with the length 

 of the cilia that, unless we assume as Verworn ('90, p. 173) does 

 that the whole base of the plate is surrounded by cilia, I see no 

 way by which the mechanical disturbance made by the cilia on one 

 side of the root of the plate could influence those on the other 

 side and thus effect transmission. As I have never seen in Mnem- 

 iopsis any reason to believe that the plates are surrounded at their 

 bases by cilia, I do not believe that transmission can be accounted 

 for in the present experiments by the mechanical theory, even 

 admitting the presence of cilia between the plates. 



A modification of the experiment just described has been 

 employed by Verworn ('90, p. 171) with the view of testing further 

 the nature of transmission. This experiment consisted in restrain- 

 ing a plate from beating instead of cutting it off and then ascer- 



