MANTON COPELAND. 



all the cilia discernible were either quiescent or showed but slight 

 activity over local areas. The behavior of the pedal cilia of an 

 adult Pollnlces is unquestionably like that of the immature, for 

 when the progression of one is suddenly prevented by holding back 

 the shell, the mucus on the bottom of the foot is driven posteriorly 

 by the beating cilia and objects such as sand grain, pieces of filter 

 paper or even a pin are swept along with it. If now the snail is 

 removed from the water, the propodium may be extended and 

 moved about, at which time the mucus glides over the entire ventral 

 pedal surface and the flicker of beating cilia can be plainly seen by 

 the use of a lens. On the other hand, if the animal is quiescent, 

 either in the water or when held out of it, there is no movement of 

 mucus and in the latter position no indication of ciliary activity is 

 distinguishable. 



Polinices placed upside down in a dish of sea water shows a 

 righting reaction which is characteristic. The tongue-like pro- 

 podium is extended, and the tip directed downward and backward 

 until the ventral anterior margin of the foot is applied to the glass. 

 The attached surface of the propodium is then advanced until the 

 inverted shell lies over the right anterior border of the foot. If 

 the animal does not succeed in applying more of the surface of the 

 foot to the glass, the shell and posterior part of the foot move 

 backward as the propodium progresses, the whole body tending to 

 circle clockwise. If during this activity sand grains are sprinkled 

 over the foot, they are carried posteriorly with the mucus by the 

 beating cilia. No muscular waves are to be seen on the portion 

 of the propodium which is adherent to the glass and locomotion at 

 this time is evidently accomplished by the cilia. On failing to right 

 itself the snail rests with the propodium still in contact with the 

 substrate, or more frequently with the organ withdrawn and held 

 in a somewhat contracted condition with its ventral surface up- 

 ward. Sand grains now remain on the foot where they are placed 

 and there is no movement of mucus. When, however, the righting 

 activity is resumed the sand and mucus again move down the foot. 

 The righting of the body is finally accomplished after more of the 

 pedal surface is applied to the substrate, particularly that portion 

 along the right side posterior to the propodium, when the rest of 

 the foot and the shell are thrown over to the left. The expanded 



