XVlll 
INTRODUCTION. 
supported by his careful researches on the origin and nature of 
ovicells. 
Thus, considering first the Cheilostomatous ‘ ooecia,’ Dr. Harmer 
has remarked that these structures are “probably not homologous 
with those of Cyclostomata”*; for, as he points out, an ooccium 
or ovicell in a Cheilostome is probably an appendage of a zooecium 
and not a modified zooeciura. 
The second term, ‘ gonoecium,’ has long been widely accepted 
for a Cyclostomatous ovicell which is developed from a single 
expanded zooecium. Thus Dr. Harmer, in his paper on “Embryonic 
Fission,” describes the ovicell as “indeed merely a modified 
zooecium, as is shown by the method of its development, as well 
as by its internal structure.”^ Ovicells wliicli are derived from 
the expansion of simple zooecia, and are therefore true gonoecia, 
occur in the genera Crisia and Entalophora. 
The third term, ‘gonocyst,’ was proposed for the ovicell which 
differs from a gonoecium, as it is not due to the modification of 
a single zooecium. The original definition is as follows : “A form 
of marsupial chamber produced by expansion within the zoarium, 
and not by the modification of a single zooecium.” Berenicea 
parvituhdata (Cat. Jur. Bry. PI. IV. Fig. 5) was then quoted 
as an example. Dr. Harmer,® however, objects that “the ovicell 
is probably a modified zooecium in all Cyclostomata.” But the 
essential difference between gonoecia and gonocysts appears to 
be established by Dr. Harmer’s own careful researches on 
‘ Lichenopora ’ verrucaria, described in a memoir published shortly 
after the issue of the Jurassic Catalogue. 
It has in fact been long recognized that the ovicells of 
Cyclostomata include two distinct types of structures. Thus Smitt 
proved the ovicell of ‘ Lichenopora ’ verrucaria to be a chamber 
formed from interstitial, i.e. interzooecial, spaces, and not from 
zooecia.^ It is also implied in his account and figures of a 
^ S. F. Harmer. “On the Occurrence of Embryonic Fission in Cyclosto- 
matous Polyzoa ” : Quart. Journ. Micro. Sci. vol. xxxiv. pp. 199-241-, 1893 ; 
see p. 233. 
2 Ibid. p. 204. 
2 S. F. Harmer. Proc. Camb. Phil. Soc. vol. ix. 1896, p. 211. 
* F. A. Smitt. “ Kritisk forteckning ofver Skandinaviens Hafsbryozoer ” : 
Ofvers. k. Yet.-Akad. Forhandl. 1867, vol. xxiii. p. 479. 
