LOCOMOTION IN GASTROPODS. 135 



hyaline membrane. This high rate of movement is always 

 associated with muscular contractions. Why it was that 

 Alectrion trimttata sometimes moved so swiftly was never fully 

 understood until I had witnessed in this way the possibilities of 

 ciliary motion. 



The third stage of ciliary activity is seen as a rule a number of 

 hours later, often about twenty-four hours after the foot is 

 severed from the body. At this time all muscular movement 

 has ceased and the whole foot has become expanded. The cilia 

 are beating everywhere at moderate speed, and if a given area 

 is watched, no variation in the rapidity of movement is observed. 

 The contrast between this uniform rate of ciliary movement 

 and the preceding highly variable one is very striking. The cilia 

 continue beating until maceration sets in and the epithelium 

 begins to break down. 



Having determined from a series of tests that the ciliary activi- 

 ties described above occurred with remarkable constancy, a 

 means was sought of controlling muscular contractions without 

 directly affecting the cilia. Previous experience had shown 

 that magnesium sulphate is an excellent anaesthetic for marine 

 gastropods and one that appears to leave no undesirable effects. 

 It proved to be equally valuable in the study of ciliary behavior. 

 When a foot of Alectrion trivittata in which muscular movements 

 are going on is placed in a ten per cent, solution of magnesium 

 sulphate made up in sea water, all contractions cease in a few 

 minutes and the foot remains passive. The cilia, however, 

 which are vigorously beating when muscular activity subsides, 

 continue to do so for many hours with only gradually decreasing 

 speed, whereas those which are quiescent remain so. Moreover, 

 if there is initial variation in the rate of ciliary movement in 

 different parts of the anterior border of the foot, it is maintained, 

 and the cilia beating the fastest remain active the longest time; 

 but changes in the speed of ciliary movement over a given area, 

 which are so striking when the foot is in sea water and muscular 

 contractions are in progress, never occur after contractility is 

 inhibited by magnesium sulphate. It is also clear that those 

 cilia which are moving most rapidly, or w r ith the least interrup- 

 tion, when the foot is in sea water tend to beat the fastest when 



