current of 1.25 to 7.6 cm /sec. stimulates the oyster drill to turn immediately 

 into and move against it. The speed of the current does not affect the rate of 

 creeping, although in swifter currents more work is performed in crawling Faster 

 currents stimulate the drill to turn into it more rapidly. Removal of eyes and 

 tentacles does not interfere with the rheotac&e response. JJtauber (1943) in a 

 simplified flow chamber determined that at current velocities as low as 0.2 

 cm. /sec Uro salpi nx no longer exhibits a positive response to current and may 

 even move down stream. At increased velocities such as those employed by 

 Federighi prompt orientation occurred. 



In Delaware Bay both Sizer (1936) and Stauber (1943) discovered in water 

 at least 6 feet deep that drill trapping is no more effective in lines of traps placed 

 at right angles to the current than in those parallel to it Sizer comments that 

 frictional forces on these bottoms greatly reduce current velocities at the level 

 of the drill and may explain the lack of response. Stauber emphasizes the fact 

 that on most oyster planted grounds the roughness of the bottom probably not only 

 greatly reduces current velocities in the immediate microenvironment of the drill 

 but also establishes local eddy currents which tend to promote aberrations in the 

 response of the drill to the main overlying flow of the current . In a migration 

 experiment on smooth sandy intertidal bottom he did find that out of a total of 164 

 drills recovered, 72% moved in the directions of the tidal flow, and 28% at right 

 angles to the flow. Galtsoff et al. (1937) in further migration studies in Delaware 

 Bay noted that oyster drills moved against the curreBft to some extent toward drill 

 traps over bottom devoid of oysters . Haskin (1937) in careful studies in an inter- 

 tidal area in Delaware Bay found that the oyster drill exhibited great variability in 

 rate and direction of movement over the bottom,, and tbsf^flirectian of current flow 

 and the position of oysters were the primary factors in determining the orientation 

 of the drills . 



Tidal currents are also of considerable importance in the dispersal of 

 young drills on floating objects, and in the transportation of chemical substances 

 emitted by prey which aid the drill in the location of food. 



Gravity 



Federighi (1931c) in studies at Hampton Roads, Virginia, discovered that 

 drills exhibit a pronounced negative geotaxis, creeping upward when the tempera- 

 ture of the water rises above 10°C This response is especially evident during 

 the breeding season. Federighi noted that the response persists in a dark room, 

 and with the eyes removed; and is not dependent on oxygen. Further, on a vertical 

 glass plate turned as a wheel on a hub the snail always turns so that the siphon 

 points up. Galtsoff et al. (1937), Stauber (1943), and the writer have noticed that 



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