USE OF THE FOOT IN SOME MOLLUSKS 363 



SO that the foot must be folded together longitudinally before 

 it may be withdrawn into the shell. When disturbed sufficiently 

 to induce retraction of the foot, the right half of this organ is 

 retracted first. 



Withdrawal of the foot is very readily induced by even mod- 

 erate stimulation; this is correlated with the condition that the 

 foot is never very firmly attached to a substratum. Only with 

 difficulty can a Conus attach the foot to a glass surface firmly 

 enough to right itself when the shell aperture has been placed 

 dorsally. Nor can the animal usually creep up a smooth surface 

 inclined at an angle of more than 60°. The foot is conspicuously 

 a burrowing organ, and is in this respect very efficient. At 

 extremely low tides, Conus may be found on sandy beaches bur- 

 rowing vertically into the sand, the spire being uppermost. 

 This is accomplished by means of a clockwise rotation of the whole 

 animal, the foot doing the work of excavation. 



In spite of the fact that the foot of Conus is large enough to 

 make observation an easy matter,^ and of the further fact that 

 the positive phototropism of the animal may be used to induce 

 it to creep with some rapidity (1.3 cm. per minute at 19°), neither 

 when the animal is creeping in air nor when submerged in sea- 

 water have I been able to distinguish wave motions upon the 

 pedal surface. In view of the powerful musculature of the foot 

 and of its bilateral control in retraction, such movements might 

 have been expected. Locomotion is, however, accomplished by 

 a smooth gliding movement. No cilia can be demonstrated upon 

 the foot, although there is abundant mucus, through which ad- 

 hesion is mainly effected. Distinct variations in the rate of 

 movement on the foot can, however, be detected along the an- 

 terior edge and at the sides. The foot is marked by longitudi- 

 nally disposed pigment flecks, which would make the detection of 

 rhythmic waves relatively easy. There seems no doubt, then, 

 that Conus affords a second instance of that type of pedal locomo- 

 tion which Parker ('11, p. 158) characterized as arythmic, with 



^ It was necessary, of course, to study the locomotion by means of observations 

 from beneath, the animals being in a broad glass dish. 



