5 o/oo, In 10 o/oo a few shelled veligers were still alive on the 42nd day, but no 

 hatching had occurred. In 15 o/oo normal drills started hatching on the 20th day. 

 In salinities over 15 o/oo normal drills were seen on the 16th day. 



These experiments indicate that lower salinities suppress the rate of 

 development particularly of the youngest stages to the point of death, and that 

 salinities higher than 10 o/oo are required for complete development of the egg 

 case stages in Delaware Bay. 



PH 



Sizer (1936) writes that Uro salpinx is viable over the same pH range in 

 which it moves . In Delaware Bay he obtained no correlation between numbers of 

 drills and pH of the seaw^ater in which they were taken. In the laboratory they 

 remained active over the range of 6.5 to 9,1, surviving at least one week in sea 

 water of these hydrogen ion concentrations. He found some evidence suggesting 

 that the drill moves less rapidly in the more alkaline and in the more acid ex- 

 tremes of this range . 



Temperature 



The activities of LL cinerea are strikingly influenced by temperature . The 

 "critical temperatures" at which its different biological activities have been stated 

 to begin and cease in a given geographic region may not be as constant for all in- 

 dividuals in a population as has been suggested (Table 13). The thermal limits 

 between which at least some of its functions are carried on seem to vary 

 inherently in different individuals, and possibly in different stages of the life 

 cycle . In addition the range of these limits may be affected differentially by the 

 interplay of associated environmental factors and thus may vary inter- and intra - 

 seasonally in the same geographic region . Finally, a number of investigators 

 have demonstrated that in many, but not all, instances the minimum thermal 

 limits above which such physiological functions as locomotory movement, drilling 

 and feeding, and opposition occur, decrease northward in the latitudinal distribu- 

 tion of the species . 



Movement and hibernation 



As the temperature of the water drops, creeping rate in the oyster drill 

 gradually decreases until at a low temperature range, which seems to vary among 

 different drills in a given region and in drill populations in different regions, 

 movement ceases altogether. A number of studies by Adams (1947), Cole (1942), 

 Engle (1935 36), Federighi (1931c), Galtsoff et el. (1937), Gibbs (pers. com.), 



70 



