decrease in the rate of locomotion occurred shortly after this . In all cases the 

 average rate of movement of the fastest moving individuals steadily declined 

 toward the group level as time of creeping from the time of liberation increased . 

 This is an important consideration which other investigators have overlooked. 

 Neglecting burrowers and obvious laggards Haskin obtained an average rate of 

 movement of 21 feet per day for the bulk of the liberated drills in a period ranging 

 from 2 to 7 days in the 6 experiments; and in the same period an average of 32 

 feet per day fcr the few farthest ranging individuals. Maximum distances covered 

 by the latter in individual experiments in periods of 2 to 3 days averaged 58 feet per 

 day. The maximum distance covered by any single drill during the first 24 hours 

 was 92 feet ; but Haskin found that these far ranging drills were transported in 

 large part by hermit crabs (see later, this section). He also noticed that a large 

 proportion of drills burrowed into the bottom and remained completely covered for 

 several days . This would account in part for the low recovery of released drills . 



The most recent studies on drill migration have been performed by Stauber 

 (1943) who also emphasized the distance covered by the majority of a migrating 

 population, He, like Haskin, believes this is important since transportation of 

 drills by other animals may explain some of the extreme values reported by 

 Fedenghi and by Engle. Stauber 1 s first experiments were performed on relatively 

 clean sandy mud bottom just below low water mark in Delaware Bay. During the 

 five trials reported the water temperature ranged from 23 to 25 "C. Drills dipped 

 in pigment were released in the center of a square mostly during high water, and 

 the extent of their movements was checked some 14 to 20 hours later at low water . 

 Oyster baited drill traps were placed at the corners of the square. Eighty -two 

 percent of the 563 drills used in the observations were recovered, and the majority 

 were found buried just beneath the sand attached principally to the tubes of a burrow- 

 ing worm. In all, 91% of the recovered drills moved less than 10 feet in the 14 to 

 20 hour period . 



From September to November Stauber utilized the same quadrat for 6 more 

 trials in which marked drills were left undisturbed for a period of one week . The 

 temperature of the water continued to drop during the experiments . Of a total of 

 445 drills placed in the square, 14% failed to move 10 feet and 47% crawled to and 

 were recovered almost exclusively in the drill traps . 



The following fall L. Jeffries working with Stauber carried out a drill 

 migration study in deeper water on bottom ordinarily utilized for oyster farming 

 but free of oysters at the time of the experiment. An area roughly 800 feet square 

 was staked and 1, 979 marked drills were released in the center. Three hundred 

 and eighty one oyster baited drill traps, which were tended weekly for a period of 

 two months, were stationed along the boundaries of the square , During the first 



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