14 
its basal part is calcified, whereas it is completely calcified in Bugula 
flahellata and Bicellaria ciliata. In Cellulariidae, both layers are 
calcified, and tbe ooecinm is in its whole lengtli firmly connected 
with the front wall of the distal zooecium. As an exemple we will 
shortly describe the development of such an ooecinm in Scrupocel- 
laria scabra ^). At a point of time when the front wall of the di¬ 
stal zooecium is still wholly membranous a calcified plate, which Ave 
will name the endoooecial plate, grows out from the margin of the 
distal wall and soon filis up the space between the calcified lateral 
walls outside the membranous front wall in the lower part of the 
distal zooecium. Next two processes from the lateral walls meet 
over the endoooecial plate which is now surrounded by a calcified 
frame, the first beginning of the ectoooecium, and finally both the 
endoooecial plate and the surrounding frame grow out from the 
zooecium in order to form the vaulted part of the ooecium. The 
back-wall of the ooecium consequently consists only of a single 
calcified layer belonging to the endoooecium. In Onchoporidae the 
ooecia are also with their back-wall firmly connected Avith the front 
wall of the distal zooecium, but the ectoooecium is wholly mem¬ 
branous. 
Hyperstomial ooecia with a cryptocyst. These ooecia are al- 
Avays covered Avith a membrane, continuous Avith that investing the 
front Avall of the zooecium and corresponding with the ectoooecium 
in the former group. The calcified part of the ooecium in many 
cases consists of tAvo distinet layers (f. i. in. Memhraniporidae^), 
Crihrilinidae, Reteporidae, Ramphostomella etc.) of Avhich the inner 
is the endoooecium while the outer must be regarded as the cryp¬ 
tocyst of the ectoooecium as it takes its origin from the cryptocyst 
V Gr. M. R. Levinsen, Op. cit. pag. 26, Tab. 1, Tig. 21, a—h. 
lu some Membraniporidae f. i, in M. unicornis, M. imbelUs, M. 
aurita etc. the ectoooecium does not cover the whole of the endo- 
* 
ooecium the lower part of Avhich can be seen as an area of different 
shape separated from the ectoooecium by the more or less projecting 
lower margin of the later. 
