ON THE DEVELOPMENT OE TUBULIPORA. 8B 



feature of this species, was developed on precisely the same 

 type. 



A case of the abnormal development of four contiguous ovi- 

 cells has been described by me (13, p. 166, pi. xii, fig. 13) in 

 Crisia ramosa. These cases are interesting as showing the 

 essential similarity of the ovicell and the zooecium. The pro- 

 duction of an ovicell is probably induced by the development 

 of an embryo from one of the eggs which so commonly occur 

 in young zooecia, most of which do not ordinarily become 

 fertile. 



The simple ovicells of the specimens of T. flabellaris 

 from Barents Sea are similar to those which were figured by 

 Savigay (37, pi. vi, figs. 4.2 and 5.2), and described by Audouin 

 under the names of Proboscina Boryi, and P. Lamou- 

 rouxii. Ovicells of a similar type are known in Diasto- 

 pora suborbicularis, Hincks, and in many fossil forms. 

 They are figured, for example, by Gregory (12, pi. i, fig. 6; 

 pi. iii, fig. 3), and this type of ovicell is given by Walford (41, 

 p. 73) as a characteristic of his genus Pergensia, although I 

 cannot agree with him in thinking that the character shows 

 any approach to the Cheilostome genera Lekythopora and 

 PcEcilopora. It appears to me probable that the stunted 

 specimens of T. flabellaris above described have reverted to 

 a more primitive condition (a conclusion borne out by the 

 evidence of fossils) in developing a less complicated form of 

 ovicell than is usually produced in other recent species, and 

 even in T. flabellaris itself. This reversion may be re- 

 garded as due to the small size of the colony, in conjunction 

 with the successful development of primary embryos in several 

 contiguous zooecia. It is probable that this points to a time 

 when the ovicells were ordinary zotecia, and that the restric- 

 tion in the number of fertile zooecia now so characterisiic of 

 Cyclostomes is not a primitive feature of the group. 



References to the oceciostome in any form hitherto described 

 as Tubulipora or Idmonea are curiously rare; and most 

 authors do not seem to have considered the possibility of the 

 occurrence of this essential part of the ovicell. Smitt (40) 



