PROGRESS IN BIOLOGICAL INQUIRIES, 1935 423 



proved to be active over the wide pH range of 6.5 to 9.1. At the 

 acid and alkaline extremes a slowing up of activity was apparent. 



Observations made in the laboratory during the wdnter months 

 on the effects of temperature on drill movement showed some loco- 

 motion even at the low temperature of 2.2° C. The rate of feeding 

 and consequently the destruction of oysters by the drills increases 

 with temperature. The interval between feeding periods varies from 

 5 to 12 days. One drill w ill destroy, on the average, 0.34 oyster per 

 week during the summer months, this estimate being lower than 

 that reported at Beaufort, N. C. The salinities and temperature in 

 New Jersey waters are somewhat lower than those at Beaufort, but 

 this would probably not entirely account for tlie appreciable 

 difference in rate of destruction at the two places. 



Below a salinity of 10 to 12 parts per mille, the drills are inactive 

 in boring the shells of oysters. Above this critical point there is 

 no appreciable change in activity with the increase in salinity. Sal- 

 inities between 10 and 15 and 30 and 35 reduce vitality of drills, 

 W'hile life cannot continue in salinities below 10 and above 35. 



As a result of winter observations the following conclusions can 

 tentatively be drawn: (1) Drills do not burrow in the mud during 

 the cold period; (2) they do not seek cavities or empty shells as a 

 place to hibernate; (3) they become dormant during extreme low 

 temperatures (2.2° C or lower) and remain on the surface of the 

 bottom. 



Experiments using bivalves of equal ages as bait failed to show 

 that the drills select those having the thinnest shells. If mussels 

 {Myfihis edulis) whose shells are thinner than those of oysters are 

 2Dlaced in a trap along with oysters as bait, the drills w^ill attack the 

 mussels first. It has been shown, however, that this preference is 

 not owing to the thinness of their shell but to the fact that the meat 

 of the mussel is preferred to that of the oyster. Consequently, 

 mussel bait is twice as efficient for catching drills as oyster bait. 

 Drills prefer the young spat to 1-year-old oysters, a reaction due not 

 to the thinness of the shell, but probably to a difference in the 

 chemical nature of the exudations of oysters of different ages. 



Urosalpinx and EupJeura have been found to be equally destruc- 

 tive, although the latter is much more active in oviposition. This 

 fact is especially important in view of the rapidly increasing ratio 

 of numbers of Eupleura to Urosalpinx on the New Jersey oyster 

 beds. 



Urosalpinx cinerea deposits an average of 8 eggs per case and 

 Eupleura sp, lays an average of 22 eggs per case. The bimodal 

 frequency curve obtained for the number of Eupleura eggs per case 

 indicated the possibility that two distinct varieties of snails of this 

 genus were encountered. Further work will have to be done before 

 this problem is solved. No significant variations in the number of 

 eggs per case as related to salinity are apparent. 



It has been found that adult drills can survive under environmental 

 conditions in wdiich they cannot reproduce. Drills placed in a trap 

 and kept for a month in water wdiere at low and high water the 

 salinity varied from fresh water to 7 or 8 parts per thousand but 

 frequently remained at or near the zero point throughout tl\e entire 

 tidal cycle survived, although no oviposition took place after the 

 first week. 



