NEUBOID 'TRANSMISSION 73 



sion wave in ctenophores than the movement of the cilia 

 is for a like wave in ciliated epithelia. 



When a row of plates in a Mnemiopsis pinned out in 

 seawater has passed under it a metal tube of small cal- 

 iber and is chilled by running water at 4 to 5 C. through 

 the tube, the plates in the region subjected to the cold 

 cease to beat, though transmission waves may be seen 

 to arrive at one edge of the cooled area and to emerge 

 at the opposite edge with regularity. Again the swim- 

 ming plates resemble cilia in that in an area in which the 

 plates have been rendered quiescent by chilling transmis- 

 sion is still possible. 



In handling specimens of Mnemiopsis in the experi- 

 ments last described, it was noticed that when the rows of ' 

 plates under which the metal tube passed were subjected 

 to a little local stretching by the awkward manipulation of 

 the tube, the plates often ceased to vibrate in the stretched 

 region. On repeating this operation it was found that 

 as a rule the slight stretching of the band of tissue to 

 which the plates were attached would bring the plates 

 of the stretched part to a standstill, though it did not 

 interfere seriously with transmission. In such an oper- 

 ation, however, much care was required not to overstrain 

 the tissue, for otherwise a permanent cessation of action 

 followed. Avoiding this difficulty, however, mechanical 

 strain, like low temperature, may be made to check 

 motion without interfering with transmission. Thus in 

 several ways the swimming plates of the ctenophores 

 exhibit all the peculiarities of rows of cilia (Parker, 

 1905 6). 



The bands of tissue to which the swimming plates are 

 attached in ctenophores have been studied with much 

 care, but in no instance have nerve cells been found as- 



