The Movements of the Swimmmg-Plates in Ctenophores. 417 



plates in a ctenophore by cold and yet leave the transmitting power 

 of the row unimpaired. To test this proposition, I passed a small 

 curved metal tube through the substance of a Mnemiopsis directly 

 under one of its rows of swimming-plates and at right angles to 

 the direction of the row. The animal was anchored by being 

 pinned in a small aquarium of sea water whose temperature was 

 21° C. Normal waves of action were seen to course over the row 

 of swimming-plates under which the metal tube had been placed. 

 I now passed through the tube water of a temperature between 

 4° and 5° C. A steady flow was kept up to insure as complete a 

 chilling as possible of that portion of the row under which the tube 

 went. The chilled plates soon ceased to move and the waves 

 appeared to jump from the aboral side from which they approached 

 the chilled region to the oral one beyond it. Sometimes half a 

 dozen waves in rapid succession appeared thus to jump this 

 chilled region. But the best evidence was obtained when the 

 waves ran at considerable intervals, at which times the correspond- 

 ence between the parts of the wave in front of and behind the 

 chilled region was most striking. To be certain that there was 

 no movement of cilia or plates in the chilled region, a small 

 amount of powdered carmine in sea water was placed on the plates 

 of that portion. The carmme remained motionless while wave 

 after wave ran over the aboral and the oral parts of the row. At 

 the close of the experiment the chilled region was allowed to 

 regain its normal temperature, whereupon its plates became 

 vibratile again and the waves passed without interruption. This 

 experiment was repeated on six different individuals and with 

 constant results. In one instance the temperature of the water 

 used for chilling the tissue was 8.5° C. and under this condition 

 the cessation of movement was only partial, but in all other experi- 

 ments the temperature was kept at 5° C. or lower with the result 

 that complete cessation of movement invariably followed. Hence 

 it is fair to conclude that in Mnemiopsis a temperature of 5° C. 

 or less will check the movement of the swimmmg-plates without 

 essentially altering the transmitting power of the row. 



In handling ctenophores in the experiments last described, I 

 noticed that when the row of plates under which the metal tube 

 passed was subjected to a little local stretchmg by the awkward 

 manipulation of the tube, the plates often ceased to vibrate in the 

 stretched region. On repeating this operation I found that as a 



