CILIARY AND MUSCULAR LOCOMOTION. 141 



diameter being separated from the surrounding portions near the 

 center of the foot. Again the ciliary action over the isolated part 

 was coordinated with that of the rest of the pedal surface. These 

 experiments prove that impulses exciting ciliary action may be 

 transmitted elsewhere than through epithelial cells, and point to a 

 subepithelial or nervous pathway. Other tests on two examples of 

 Polinices hcros substantiated this view. The tissue lying beneath 

 the epithelium was severed in a plane parallel with the surface. 

 The cuts extended inward from near the border of the foot poste- 

 rior to the propodium, leaving most of the overlying epithelium in 

 contact with that of the rest of the foot, but isolating it from the 

 deeper portions of the organ over an area, in one case, about 15 

 mm. long by 4 to 7 mm. wide, and in the second instance, approxi- 

 mately 8 mm. by 13 mm. Many tests were made during righting 

 reactions, and although sand grains moved with the mucus directly 

 in front and back of the areas cut under, and also to one side of 

 them, they remained quiescent over the isolated regions themselves. 

 The operation caused the epithelium to become somewhat con- 

 tracted, but numerous tests on normal individuals have shown that 

 a wrinkling of the pedal surface does not in any mechanical way 

 inhibit the beating of cilia. 



CONCLUSIONS. 



The view that gastropod locomotion is not always a muscular 

 process is well supported by the behavior of Polinices where two 

 types of progression occur in a single species, one of which is im- 

 mediately recognized as muscular, whereas the other presents en- 

 tirely different features and upon analysis appears to be dependent 

 on ciliary action. 



The general ciliary behavior in Polinices, and especially the re- 

 sults of the experiments just described, uphold strongly the con- 

 clusions already drawn from a study of two species of the genus 

 Alech-ion, namely, that the control of ciliary action has been taken 

 over by the nervous system, perhaps directly, or conceivably 

 through connections with muscle or mucous cells associated with 

 the ciliated cells. Intraepithelial transmission may play some part 

 in effecting the spread of ciliary action, but evidently impulses 



