Late warm periods in the fall Slave been the apparent cause of a number 

 of unusually late spawning records, T C. Nelson (pers. com.) once caught a 

 drill ovipositing on December 26 in New jersey during a very warm period. The 

 egg cases lacked opercula and cleavage of the eggs was abnormal. Andrews 

 (pers. com.) recently found a few egg cases with live embryos in Mobjack Bay, 

 Virginia, in February. And Loosanoff and Davis (pers. com.) have found 

 recently oviposited egg cases in Milford Harbor as late as November 19, also 

 probably as a result of warm weather. 



The periods of maximum spawning in different areas given in Table 4 are 

 probably not comparable because no quantitative standard is given by any of these 

 investigators for "maximum" spawning. Nonetheless these periods and the dates 

 at which spawning is said to commence in various regions both appear, though 

 nebulously and with numerous exceptions, to occur earlier in the year in the 

 southern latitudes than in the more northern waters. 



Behavior of the Drill during Oviposition 



Female oyster drills generally affix their egg cases to the sides, under- 

 surfaces, and crevices of mollusk shells, cement blocks, tin cans, rocks, stakes, 

 piling (Galtsoff et al., 1937), and any other hard available surfaces which may be 

 only partially submerged, as in the lower intertidal zone, or completely submerged, 

 as on subtidal grounds. Egg case clusters rrlay also be found abundantly under 

 rocks (Pope, 1910-11). 



In addition to seeking hard surfaces for oviposition, drills generally 

 select sites which project somewhat above the surface of the bottom and which 

 offer niches tree from siltatiofc and possible burial and suffocation (Federighi, 

 1931c; Cole, 1942; Stauber, 1943). In the laboratory egg cases are most frequent- 

 ly deposited on the vertical^ sides of aquaria if no clusters of oysters or similar 

 objects are present on the bottom . 



\ 



However the presence of suitable food material may further influence the 

 selection of the spawning site. Federighi (1931c) and the writer observed that 

 drills in laboratory tanks in which living ovsters are present in almost all cases 

 crawl onto the living oysters to lay their egg cases in preference to the sides of 

 the lank.. Slzer (1936) reports that In drill trapping experiments in Delaware Bay 

 he found the upper valve of a living oyster is preferred tm the surface of an empty 

 shell for oviposition. Stauber (1943), who continued these studies, found in June, 

 1937, wlrile dredging over bottom covered mostly with shells that egg cases were 

 predominantly attached to living oysters: of 301 shells examined only one possessed 

 egg cases, and of title five large oysters in the same catch, two held egg cases. 



35 



