Similarly he found that during two successive seasons oyster baited traps 

 attracted more oviposition than shell baited traps. In 1939 during the major 

 spawning period 250 oyster baited traps caught 1.03 drills and 0.03 cluster of 

 egg cases, and 50 shell baited traps captured only 0.45 drill and 0.01 cluster 

 of egg cases per trap per week. 



As many as a dozen female drills may aggregate to spawn on one location 

 (Pope, 1910-11, Massachusetts; Cole, 1942, England; the writer, in aquaria in 

 New Jersey and in North Carolina) Cole does not think this represents a social 

 behavior but merely the occupation of a nearby available and satisfactory spawn- 

 ing site. This, however, does not seem to be the fundamental explanation; further 

 research should be performed on this interesting and significant behavior. Pre- 

 paratory to deposition of her egg cases, the drill by the use of her radula 

 carefully cleans the surface to which the egg cases are to. be attached. If 

 disturbed while spawning she may creep away, but in many cases returns in a 

 few days to the original site to resume spawning. If undisturbed she has been 

 observed to spawn continuously for as long as 7 days (Galtsoff et al., 1937; Feder- 

 ighi, 1931c) . Federighi noticed that sudden drops in temperature or lifting the 

 drill from the substratum stops spawning 



In an effort to study the relation between the quality of food which drills 

 eat and fertility, Galtsoff et al. (1937) placed lots of 10 drills each in tanks 

 supplied with running sea water containing a variety of food animals. It is not 

 stated how the sex of these drills was determined or how many were immature 

 females. The authors conclude because they obtained considerable variation in 

 the number of egg cases deposited that fertility in drills is correlated with the 

 quantity and quality of food. On the basis of Stauber's (1943) data on the relation 

 of size and maturity of drills to oviposition, and because there is no assurance 

 that all 10 drills in each experiment were females (many may have been males), 

 some doubt is cast on these results . Nonetheless, as Stauber states, the quantity 

 and quality of food probably do influence oviposition. Although Pope (1910-11) 

 noticed no cessation of feeding of a number of drills during the entire spawning 

 season from June 1 to August 1, it is true that females do not feed during the 

 actual process of oviposition (Federighi, 1931c; the writer, unpub.), and probably 

 feed more rapidly after spawning. 



Egg Case Stages 



After the egg case is affixed to the substratum drills exhibit no concern 

 for the young. Egg cases are abandoned and the developing young, which pass 

 all the larval stages within the egg case, care for themselves. The absence of 

 a planktonic stage, though limiting rapid dissemination, has not appreciably inter- 

 fered with the success of this animal. If anything, the protective confines of the 

 egg case support a high rate of survival of the young. 



36 



