THE MORPHOLOGV OF THE CHEILOSTOMATA . 301 



interior of the spherical ovisac, wliile the ovary still remains 

 in its original position. 



My preparations do not enable me to trace the origin of 

 the egg-containing sac, which may, however, be a diverticulum 

 of the vestibule, as described l^y Cnlvet (1000, fig. 42, on 

 p. 2GG) in Lepralia pallasiana. 



The conclusion pointed to by these facts is that the dimor- 

 phism of tlie opercula indicates the derivation of the species 

 from forms provided with ovicells ; in which, as is well 

 known, the operculum of the fertile zooecium is commonly 

 larger than that of the other zocccia. 



F 1 u s t r a c r i b r i f o r m i s, Bnsk.^ 

 This species is introduced at this point in further illustra- 

 tion of the morphology of the ovicell. Its frontal wall is, of 

 course, typically Flustrine. The ovicell is of the type usually 

 described as "internal,"- and is merely represented by a 

 more or less hemispherical bulging of the distal zooccial wall 

 into the next zooccinm. Into this space projects a spherical 

 vesicle, which lies just beneath the vestibule, as in the fore- 

 going species. The polypides are retracted to the extreme 

 proximal end of the zooecium. In some cases I have been 

 able to detect a very small ovary in one of the proximal 

 corners of the zooecium, near the basal wall; but in conse- 

 quence of the position of the polypides I cannot say whether 

 the ovary is parietal or attached to the polypide. The egg 

 enters the spherical sac, in some manner which has not been 

 observed, while it is still very small. It receives its yolk while 

 in the sac, and when it is full grown it is so large that with its 

 investing sac it occupies as much as half of the bodj'-cavity. 



Sell izop ore 11a linearis,^ Hass. (figs. 48, 52). 

 The characteristic " sinus " or projecting proximal tongue 

 of the operculum of this genus is very similar to the part of 

 the operculum which in certain species of Lepralia occurs 



1 1852, p. 51 ; ISSt, p. 58. 



2 Cf. Levinsen (1891), p. 275. 



3 Hmcks (1880), p. 2i7. 



