provides pressure to expand the foot as the animal emerges from its shell, and 

 to evert the accessory proboscis . The artery running into the proboscis becomes 

 relatively thin walled, muscular, elastic, and capable of considerable stretching 

 commensurate with the flexibility of the proboscis . This artery funnels fluid to 

 and creates pressure within the spaces in the odontophore which supports the 

 radula. During drilling and feeding the radula is firmly supported upon the muscular 

 odontophoral cushion made turgid by the action of numerous muscles contracting 

 about the blood gorged odontophoral spaces . The proboscis as a whole is everted 

 by combined muscular activity of the proboscis walls and by pressure resulting 

 from muscular compression of the fluids in the cephalic cavity. Blood returns to 

 the heart through a system of open spaces and short vessels among the organs, 



Locomotory System 



All shelled stages of the drill are capable of a slow creeping movement 

 on the foot. The latter is a pale creamy yellow highly contractile muscular organ 

 truncated in front and tapering behind, which scarcely extends beyond the broadest 

 outlines of the shell. Federighi (1931c) observed that the drill moves by a smooth 

 gliding motion and that the contact surface is covered with cilia . He was unable to 

 detect pedal waves of muscular contraction during locomotion, and because the 

 effective stroke of the cilia on the ventre surface of the fcot is backward he sup- 

 posed that locomotion is due to then activity He noticed that at rest the snail 

 is attached to the substratum by means of the posterior portion of the foot, and 

 that when movement is initiated the anterior margin of the foot is extended forward 

 and attached. Until the front part of the foot is in contact with the substratum no 

 foiward movement can occur, He observed in the laboratory that at 26, 5° C the 

 drill crept forward at an average rate of 2 6 to 2,8 cm./min, ai d did not creep 

 backward. More recent observations suggest that drills may back into the bottom 

 when burying for the winter (Garriker, 1954). Federighi states that adhesion 

 depends entirely on the secretion of mucus as shown by the absence of areas of 

 concavity which are necessary if suction plays any part in adhesion . The writer 

 doubts, because of the unusual tenacity with which drills adhere to firm surfaces 

 and because adhesion by muscular action does not necessarily produce obvious 

 areas of concavity, that mucus is the sole agent of attachment in this case . 



Galtscff et al , (1937), also in the laboratory, and presumably at summer 

 temperatures, noticed that the drill may move either on a horizontal or on a 

 vertical surface at the rate of 2.5 cm./min., but point out that temperature and 

 salinity of the water, character of the substratum, light intensity, and water 

 currents may exercise an influence on the activities of the drill, hence its move- 

 ments are necessarily variable. 



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