284 SIDNEY F. FTARMER. 



be the case, though I have obtained some evidence pointing 

 in that direction. 



Dr. G. M, R. Levinsen has kindly given me permission to 

 alhide to his very interesting observation (which he proposes 

 to publish hereafter), that in Alysidium parasiticum, 

 Busk/ the ovicells develop as two arched, hollow valves, 

 corresponding with the oral spines which occur on the 

 ordinary zooecia. I do not at present know what conclusions 

 Dr. Levinsen deduces from this observation, with which I was 

 acquainted before making my own on E. episcopalis. 



In HeterocBcium amplectens, Hincks^ has described 

 a Membranipora-like Cheilostome, in which the ovicell is 

 constitnted by a number of spines placed distal to the oper- 

 culum, which meet in a Cribrilina-like manner, and form a 

 structure which, in other respects, resembles a normal ovicell. 



Calvet (1900, pp. 57, 58, 132, pi. ii, fig. 14) states that in 

 Bngula there is a coramuuicatiou-pore between the ovicell 

 and the distal zooecium. 



It follows from the account given by Calvet and others, 

 that the cavity of the ovicell, internal to its inner layer, is an 

 external space which is overarched by the double wall of the 

 ovicell. This is obviously true in a case like that of 

 Mucronella coccinea, where the most distal oral spines 

 of the fertile zooecium are actually inside the cavity of the 

 ovicell. 



Further investigation is necessary to decide the morpho- 

 loo-ical nature of the Cheilostome ovicell. The existence of 

 three possibilities is generally recognised : — (1) That the 

 ovicell belongs to the fertile (proximal) zooecium ; (2) that it 

 belongs to the distal zooecium ; (3) that it is a modified indi- 

 vidual, as believed by Nitsche and others. The second possi- 

 bility would seem to be indicated by Calvet's observation 

 above referred to. The relation of the operculum of the 

 fertile zooecium to the ovicell, the occurrence of the " internal 



' 1852, p. 14. 



2 'Ann. Mag. Nat. Hist.' (5), viii, ISSl, p. 129, pi. iii, fi,^^ 7; iM. (G), 

 ix, p. 332. 



