(1947) terms these external metabolites "ectocrines", and Bullock (1953) extends 

 Lucas' concept to include the effective chemical signals involved in carnivorous 

 sea star and gastropod predator -prey relationships During the present century 

 it has been demonstrated that a positive chemotactic response to the external meta- 

 bolites of certain prey is also important in guiding Urosalpinx to food. It is 

 instructive to review the evolution of this concept as it applies to U cinerea . 



That smaller oysters are preferentially selected by Urosalpinx has been 

 common knowledge for some time . Pope (1910-11) and a number of workers after 

 him believed that oyster drills select the thinner shelled bivalves, but were unable 

 to explain how these bivalves are detected, Fedenghi (1931c) noted in the labora- 

 tory that drills will move toward living oysters in preference to oyster meats . 

 T. C. Nelson (Haskin, 1950) observed that drills when feeding on a population of 

 oysters of varied sizes do not always drill the smallest oysters. Many years later 

 Cole (1942) in a similar observation in England noticed that drills show a diiftinct 

 preference for spat of thumbnail size, and do not attack very small spat until all 

 the larger spat are destroyed And Stauber also (1943) reports a case in which 

 five recently drilled oysters over 3 cm . in length were found among 85 young live 

 oysters . 5 mm . in diameter in Delaware Bay . 



Haskin (1940. 1950) in laboratory studies performed during the summers 

 of 1935 and 1936 in Barnegat Bay, New Jersey, provided considerable information 

 on the degree of attraction to adult drills of substances released by living oysters 

 of varying ages , He utilized a system of tanks in which sea water from an over- 

 head reservoir, refilled at each high tide, flowed into compartments of a double 

 tank . Oysters of different ages were placed in these chambers and overflow water 

 was piped to opposite corners of a rectangular flat dish in the center of which 

 experimental drills were grouped. Since Federigm (1929) demonstratedCiat drills 

 move against a current of water, Haskin observed special precautions (not described) 

 to eliminate the effect of current so that drills would orient only to substances from 

 the oysters in the overflow water. In an extended series of observations he demon- 

 strated conclusively that substances released by oysters and carried in sea water 

 definitely attract oyster drills . He further demonstrated that water from one year 

 old oysters is more attractive to Urosalpinx than that from two and three year old 

 oysters; and water from two year old oysters is more attractive than that from 

 three year olds. Oysters three years old or older are not distinguished from each 

 other. 



In the early summer of 1937 Haskin (1950) extended his laboratory studies 

 to field investigations on a sandy mud intertidal flat m Delaware Bay, Groups of 

 oysters were placed in opposite corners of a 10 foot square . Marked drills were 

 planted in the center and their positions were recorded during the following low tide . 



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