74 THE ELEMENTARY NERVOUS SYSTEM 



sociated with them in such a way that their ordinary 

 powers of transmission and polarization could be attrib- 

 uted to these elements. It seems likely that transmission 

 along the bands of plates whereby their metachronism is 

 maintained is accomplished through the epithelial cells 

 that compose the bands as it is in the rows of cells in cili- 

 ated epithelia. 



Although this view of the coordination of the swim- 

 ming plates of ctenophores agrees well with the estab- 

 lished facts in the case, it must not be forgotten that evi- 

 dence has been brought forward to show that these plates, 

 unlike ordinary cilia, are under some nervous control and 

 that in this respect they represent a more complex state 

 of affairs than that seen in ordinary ciliated epithelium. 

 This evidence has been produced by Bauer (1910). If a 

 swimming Beroe is gently touched in the region of the 

 mouth, its swimming plates momentarily cease moving. 

 If it is vigorously stimulated in the same region by being 

 stuck or cut, for instance, its plates act for a short time 

 more vigorously than usual. Thus a slight stimulus pro- 

 duced inhibition, a considerable one excitation. If now 

 the sense body at the aboral pole of the animal is cut out, 

 thus removing what is usually assumed to be the chief 

 coordinating center for the activity of the rows of plates, 

 the same reactions in the plates recur on applying the 

 appropriate stimuli to the region of the mouth. Bauer, 

 therefore, believes that since these reactions can not be 

 ascribed to the aboral sense body they must depend upon 

 the action of the diffuse nervous system which has long 

 been known as a subepithelial network and which, though 

 chiefly concerned with the muscles of the ctenophore, 

 probably also exerts a secondary influence on its rows of 

 swimming plates. Thus the nervous control of the swim- 



