in egg cases; such abberations seem most likely to occur during the initial 

 attempts at oviposition in the life cycle of the drill. Haskm s (1935) data in 

 Table 2 is based on a collection of 1, 297 egg cases in Cedar Creek, Rarnegat 

 Bay, New Jersey., between June 20 and July A., 1935 Cole : s (1942) figure of 

 117 for the average number of eggs per case, was computed from a collection 

 of 1, 423 egg cases from different localities and is similar to Brook's (1879 1880) 

 figure. Stauber's data would suggest that these high figures may have resulted from 

 collections of egg cases oviposited predominantly by larger females . Cole reports 

 that there is little variation in the number of eggs per case in eggs collected from 

 one parent; this is probably for egg cases oviposited at one stage in the life cycle 

 of the drill . The overall average of ova per case in Table 2 is 9 3 The varia- 

 tions in the reported regional averages are not excessive and may express 

 differences in age of the ovipositing females except in the English Urosalpinx 

 which because of its larger size may oviposit more ova per capsule than its 

 American relatives. 



Egg Capsule 



The egg cases of Urosalpinx are tough, leathery ; urn shaped capsules 

 which occur in clusters tightly affixed to firm substrate by means of short slender 

 sMlks whose bases unite with those of neighboring egg cases , A round lid or 

 operculum is located on the middle free end of the case and is described by Pope 

 (1910-11) as similar to a door which after the emergence of the first drill hangs 

 as if by a hinge The wall of the egg case consists of three layers: an outer tough 

 one is detachable by mechanical means; a middle layer> also tough, is transparent 

 so that by removal of the outer membrane the embryology of the drill may be 

 observed (Haskin, 1935); the innermost lay. first described by Haskin (1935), is a 

 delicate membrane which completely encloses the eggs and is present throughout 

 the development of the embryos, although it becomes invisible in the later stages 

 of development. Haskin concludes that the innermost membrane may play a major 

 role in the permeability of the egg capsule Egg cases are clear bluish white when 

 first laid but gradually change in color through yellow to a deep yellowish brown at 

 the time of hatching Ova are suspended within the egg case in a soft transparent 

 jelly-like medium which serves as a source of food and a buffer against mechanical 

 shock . 



Egg case membranes are composed of relatively insoluble protein, and are 

 permeable to the constituents of sea water as well as to a variety of foreign in- 

 organic solutions, organic salts,, and dyes, some of which may be toxic to the 

 developing drill. The cases seem to function in protecting the larvae from mechan- 

 ical injury and from predatory organisms but not from ionic changes in the 

 environment. The salinity of the contents of the egg case is much lower than that 

 of sea water and may be related to the low salinity of the prehatched drills (Sizer, 

 1936; Galtsoff et ah 1937). 



30 



