Drilling, then, involves both a mechanical and probably a chemical phase 

 in tins gastropod, contrary to Kornnga s (1952) suggestion that it is entirely 

 mechanical (made without citation of the writer's 1943 paper). Reference should 

 be made here to reports on the drilling mechanism of the boring gastropods of the 

 family Naticidae (Jensen. 1951; Turner, .1953) which indicate that drilling is entirely 

 mechanical; however, these investigations are not conclusive and should be extended 



The feeding process in the oyster drill consists of mechanical rasping of the 

 softer flesh of the prey. The proboscis is extended through the newly drilled hole 

 and the radula tears away bits of flesh with its sharp backward pointed teeth , 

 Whereas during drilling the maximum stress is placed on pressing the radula 

 against the substratum, in feeding it is directed to tearing off bits of flesh during 

 the letractor stroke . The radula is ineffective in rasping tissues like the ad- 

 ductoi muscle of adult oysters urtil they have undergone partial autolysis . The 

 teeth thus do little more than rasp free soft tissues incru station s, and softened 

 shell material , Flesh caught on the radular teeth and transported into the buccal 

 cavity is neatly removed by esophageal suet ion and then carried by ciliary and 

 peristaltic activity to the stomach at an average rate of about 2 mm /sec at 28 °C 

 Loose food materials such as mucus and oyster ova are ingested mostly by means 

 of the sucking movements of the buccal cavity and the esophagus while the radula 

 remains stationary Firm flesh is never "sucked" out of the oyster as was commonly 

 reported in the earlier literature . Objectionable particles which pass as far as the 

 esophagus are promptly regurgitated by a reversal of the movements of these organs, 

 Rasping is a slow process, and since there is no crop in the digestive system and 

 the tract is relatively small, in keeping with the carnivorous habit, the snail appears 

 to be able to digest food and shell material at the rate at which it accumulates in the 

 stomach . 



Excretory System 



The carnivorous habit of the oyster drill undoubtedly produces a 

 plentiful supply of nitrogenous metabolic waste Fretter (1946) in a brief though 

 detailed account describes an accessory, and possibly the principal, excretory 

 organ in U. cinerea . This is the anal gland, a brown or blackish tissue embedded 

 in the wall across the upper posterior portion of the mantle cavity and underlying 

 the rectum. In adults the gland is composed of a much branched system of blind 

 tubules which coalesce and empty by way of a short duct into the rectum immediately 

 behind the anus . The anal gland consists of only one type of ciliated cell whose 

 cytoplasm becomes filled with brown spherical concretions. At what appears to 

 be the beginning of a cycle these may be scattered irregularly, and later clump 

 into a few larger masses in vacuoles. These concentrations, and sometimes whole 

 cells, are expelled into the lumen of the gland and are directed toward the outside 

 via the anus by languidly beating cilia By use of trypan blue and soluble and in- 

 soluble iron saccharate Fretter demonstrated that the anal gland functions as a 



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