LOCOMOTION IN GASTROPODS. 137 



A few experiments were carried on in which the snail itself 

 was placed in a solution of magnesium sulphate. The behavior 

 of the cilia was essentially the same as it was when the foot was 

 severed from the more dorsal parts of the body. 



Although the ciliary activities on the excised foot of the mud 

 snail were not studied so thoroughly as in the case of Alectrion 

 trivittata, enough work was done to convince me that the ciliary 

 mechanism of both species operates in the same way. 



Finally a careful investigation was made of the relation be- 

 tween muscular and ciliary movements when the snail was fas- 

 tened to a support with its foot expanded at the surface of the 

 water. Here also the cilia along the anterior border were seen 

 to start beating as muscle contractions occurred, and to decrease 

 their rate of movement as the contractions subsided and stopped. 

 The lateral foot processes were sometimes swung about and this 

 movement was also accompanied by local ciliary activity. When 

 the cilia were beating actively and continuously the anterior 

 border of the foot showed a vibratory motion caused by a series 

 of rapid contractions and expansions. In addition to the more 

 local muscular contractions correlated with ciliary action, there 

 sometimes occurred irregular foot movements of greater dis- 

 tribution which were unassociated with beating cilia. Move- 

 ments of the latter type were also observed occasionally when 

 the foot was removed from the body. 



CONCLUSIONS. 



The observations and experiments briefly recorded above lead 

 me to believe that locomotion in Alectrion is the direct result of 

 ciliary action and not arhythmic muscular movements, and the 

 unusual behavior of the cilia points to the conclusion that they 

 have been brought in one way or another under the control of 

 the nervous system. The fact that a resting snail can be made 

 to move its pedal cilia by stimulating the receptors on one of its 

 tentacles with fish meat is in itself sufficient evidence of the con- 

 trolling action of the nervous system. The muscular move- 

 ments, which occur when cilia begin beating and which accompany 

 vigorous ciliary activity, may be explained by assuming that 

 efferent impulses arrive at the ciliated cells and muscles at 



