CILIARY A XL) -MUSCULAR LOCOMOTION. 133 



tongue. The remaining portion of the foot is elliptical in outline 

 and possesses a dorsal area which is reflected over a section of the 

 shell. The ventral pedal surface is covered by ciliated epithelium 

 which is richly supplied with mucus. The dorsal surface of the 

 propodium is also ciliated. The effective strokes of the cilia are 

 directed toward the posterior end of the foot and there is no indi- 

 cation that they are ever reversed. 



CILIARY BEHAVIOR AND LOCOMOTION. 



When Poliniccs is placed in a glass dish filled with sea water, it 

 usually exhibits a gliding type of locomotion quite distinct from 

 another form of progression which it sometimes employs involving 

 marked muscular contractions of the foot. The former method 

 may be considered first. A close inspection of the foot as it slides 

 over the substrate fails to reveal any indication of rhythmic pedal 

 waves, all regions of the organ moving at the same speed over a 

 thick layer of mucus. Slight muscular contractions produce a 

 rippling motion along the anterior border of the propodium. The 

 same mode of progression is seen when the snail is moving over 

 a sandy or pebbly substrate, and is essentially like that described 

 for Alectrion obsolcta (Parker, 'n ; Copeland. '19) and Alcctrion 

 trivittata (Copeland, '19), where locomotion has been shown to be 

 due to cilia beating in mucus which covers the sole of the foot and 

 adheres to the substrate (Copeland, '19) . A young Polinices hcros 

 was also noted moving in a similar manner in an inverted position 

 along a band of mucus laid down on the surface film of the water. 



In Alcctrion it was found that actively beating cilia are char- 

 acteristic of a moving snail, whereas they are quiescent, or nearly 

 so, when the animal is motionless, as would be expected if the cilia 

 function as locomotor organs. Accordingly Poliniccs was first 

 studied with the object of determining whether the behavior of the 

 pedal cilia was like that recorded for Alcctrion. An adult snail is 

 too large for successful microscopic examination, but a young indi- 

 vidual (P. heros} whose foot measured 22 mm. in length was 

 observed while moving over a slide in a small amount of water and 

 the cilia on the thin posterior portion of the foot could be seen 

 beating actively. The same animal was again examined when rest- 

 ing with a partly contracted foot in a culture slide, and at this time 



