136 MANTON COPELAND. 



the foot is removed to a solution of magnesium sulphate. If 

 now the foot is returned to sea water, muscular contractions 

 reappear in a few minutes and ciliary behavior is just the same 

 as it was before the transfer. 



These experiments indicate that the pedal cilia are normally 

 set into activity and their rate of beating is modified either by 

 the contraction of underlying muscle fibers or by direct nervous 

 impulses. The fact that cilia continue beating in a magnesium 

 sulphate solution after muscle activity has disappeared shows too 

 that they have the power like ordinary cilia of maintaining 

 movement in the absence of extra-epithelial stimulation, and 

 finally, since their movement persists until they become ex- 

 hausted or the epithelium breaks down, it is evident that they 

 depend on some extrinsic factor to bring them to rest. In this 

 connection it should be recalled that a foot which has been in 

 sea water for a long time, perhaps for twenty-four hours, shows 

 the cilia everywhere moving at uniform speed over a given area 

 in the complete absence of muscular movement. In the latter 

 case all the cilia were stimulated to movement before nervous 

 impulses and muscular contractility gradually disappeared, and 

 their behavior is the same as it is after these activities are sud- 

 denly inhibited by magnesium sulphate. When a foot which 

 exhibits no muscular contractions is placed in a ten per cent, 

 solution of magnesium sulphate the most marked change noted 

 is but a slight retardation in the rate of ciliary movement. A 

 more concentrated solution may bring about a decided slowing 

 down or even a cessation of ciliary action. This appears to 

 be a direct effect upon the ciliated cells, which show normal 

 activity again after the foot has been transferred to sea water. 



During the course of one experiment I was surprised to note 

 certain cilia beating in the magnesium sulphate solution which 

 were quiescent after the foot was placed in the solution twenty- 

 four hours previously. An examination of the foot showed that 

 it had revived during its long immersion in the fluid, and that 

 contractions, such as ordinarily accompany the movement of 

 the cilia, were in progress. Another instance of the reoccurrence 

 of muscular and ciliary activity was recorded in the case of a 

 foot which had remained in a magnesium sulphate solution over 

 twenty hours. 



