As a result of his studies Stauber concurs with Fedenghi that drill 

 migration is probably less important in influencing densities of drills on oystei 

 bottoms than other factors. Cole (1942) from his observations on the rate of 

 movement of drills in a trough and a study of the results of Fedenghi and of 

 Galtsoff et al ., concludes that it seems unlikely from the limited evidence avail- 

 able that migration is of more than local significance in the distribution of the 

 species Engle (1953) from many years of experience also concludes that the 

 drill does not migrate very rapidly. 



The data collected by various authors on migration in U. cinerea are 

 summarized in Table 15. Inspection of this reveals that drills living among 

 oysters and other food organisms move very little (Federighi 1 & 2) and that 

 drills tagged with celluloid tags move scarcely at all (Federighi 2) . The most 

 reliable data available indicates that the majority of drills on oyster bottom devoid 

 of oysters, or on clean firm bottom, tend to move at an average rate of 15 to 24 

 feet per day m the direction of food (Galtsoff et al., Haskin, Stauber 3). In this 

 connection Adams (1947) describes an instance in Canada where drills crawled 

 75 feet across barren mud bottom to a dense planting of oyster spat, but un- 

 fortunately does not report the time involved and the consistency of the bottom. 

 And Mistakidis (1951) states that in England drills favor well cultivated grounds 

 and apparently migrate actively to these from surrounding muddy bottoms. He 

 does not support his suggestion; it is more likely as other observers have suggested, 

 that drills where possible avoid loose muddy bottom devoid of food Table 15 

 further suggests that a few drills may be carried considerably distances (Galtsoff 

 et al ., Stauber 3, Ha skin) --- see later, and that sand slows the movement of 

 drills over die bottom (Stauber 1 & 2) . 



It has been mentioned that: pronounced variability of drill densities even 

 on adjacent, grounds denotes a low rate of migration. Oysters and empty shells 

 maintain a rich fauna (Norringa, 1951) and it is probable that many of these animals 

 are utilized by the drill for food. Consequently a sizeable population of drills may 

 be supported on oyster bottom after oysters grow to a size less vulnerable to drill 

 attack The writer suggests that the impetus for drills to emigrate from bottoms 

 covered with shell or with older oysters may not be as strong as has been supposed, 

 but that in the absence of food or in the proximity of an abundant supply of new food 

 drills may exhibit pronounced movements. Stauber (1943) adds that drill locomo- 

 tion is variable not only over unused bottom, but may be slowed considerably by 

 patches of mud or by unevenness due to the presence of considerable shell. 



Ha skin (1937) and Stauber (1943) contribute the important suggestion that 

 the transport of drills by other animals may account for the extreme distances 

 covered by marked drills in migration studies . Federighi (1931c) was the first to 



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