Although cloistered, not all the fertilized ova achieve full development. 

 In a general account of the early embryology of U. cinerea Brooks (1879-1880) 

 was the first to show that abnormal eggs are frequently found m egg capsules, 

 and that occasionally an advanced embryo breaks tip and these swimming frag- 

 ments are consumed by other embryos. Pope (1910-11), Federighi (1931c), 

 Haskin (1935), and Cole (1942) have confirmed these observations. 



Federighi (1941c) reported that 28 egg cases containing an average of 

 8.8 ova per case gave rise to an average of 5.1 young drills per case, suggest- 

 ing a mortality of about 42% in the waters of mid eastern Umted States . Haskin 

 (1935) working on drills in New Jersey found that approximately half of the eggs 

 laid in egg capsules failed to mature . He suggests that the existence of some 

 atypical sperm in the gonads of males may be associated with the development 

 of abnormal embryos and this has prevented unrestricted canniball£rm . Brooks 

 earlier (1879 - 18CQ) Indicated that he thought this method of feeding is an 

 accidental and exceptional one. To the writer's knowledge no one has described 

 atypical sperm in Urosalpinx . Such sperm should be looked for and, if present, 

 their relationship to prefetching mortality determined. Cole (1942) in English 

 waters observed an average mortality during incubation of 1 . 73 embryos per case, 

 or 13 .9%. Of a total of 1, 423 egg cases collected in different localities, 823 cases 

 contained shelled veligers about to hatch which averaged 10.74 per case. Cole's 

 mortality figure of 13 .9% is noticeably lower than the figures of Haskin and 

 Federighi, and since it is based on extensive field observations is perhaps the 

 more realistic; however, it is also possible that in addition a regional or a racial 

 difference is being expressed here. 



Incubation Period and Hatching Behavior 



Data on the duration of the incubation period of the egg case stages of 

 the drill reported for a number of geographic regions, both in the field and in 

 the laboratory, are summarized in Table 5. Federighi (1931c) determined the 

 incubation period in the laboratory in Hampton Roads by isolating 11 different 

 groups of freshly Laid egg cases at different intervals between May and August. 

 Haskin (1935, quoted by Galtsoff et al., 1937, without citation) in Cedar Creek, 

 New Jersey, in the field at a carefully recorded temperature range, found that 

 the first drill 3 may hatch from different clusters over a period of 18 to 31 days, 

 and that normal Late stages could still be found in some egg cases in the same 

 cluster as late as 46 to 53 days after oviposition. Stauber's (1943) data are based 

 on the first appearance of egg cases and of small drills 2-3 mm. in height on the 

 bait of drill traps in large scale field operations, and thus the duration of the in- 

 cubation period which he records is understandably longer than that of Haskin 

 (1935) even though Haskin" s observations were carried out at a slightly lower 

 temperature range. Stauber noted, as did Pope (1910-11), that in the fall at 



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