27 
Euthyris ohtecta as poiiited out by Harmer this task is performed 
by a number of calcareous processes, and in Calymmophora lucida by 
a keel running down the side-walls of tlie zooecia. In both species 
the distal wall and the wall between the neighbouring zooecia are 
perforated by a large number of single-pored rosette-plates. 
The reneival of the zooecia. Besides the well known renewal 
of the polypide a renewal also of the whole bryozoid has been 
found in a number of Bryozoa , namely in the Ctenostomatous ge¬ 
nera Valkeria, Boiverhankia and Triticella in which the old zooecia 
are deciduous and can be replaced by new zooecia taking the place 
of'their predecessors. But also in the Cheilostomata such a rene¬ 
wal can take place and the presence of a double margin in the 
zooecium of a Alembranipora is a proof that a new zooecium has 
liere been developed inside an elder one. This form of renewal 
can be compared with that found in the thecaphorous Hydroids 
in which a new hvdrothek is formed inside an elder one, whereas 
in the athecate forms the „heads“ of the hydranths are deci¬ 
duous and replaced by new ones in the same manner as the 
zooecia in the above ctenostomatous genera. Besides in a few 
recent species I have found double (or sometimes triple) mar¬ 
gins in numerous cretaceous species of Alembranipora and such 
double-margined zooecia have been figured by several authors, for 
instance by d’Orbigny^). In regard to this renewal we can 
discern four different cases, found in the species examined: 1) a 
new zooecium can be developed in an old one, 2) an avicularium 
can be developed in an old zooecium, 3) a new avicularium can 
be developed in an old one and 4) a zooecium can be developed 
in an old avicularium. Besides in Membranipora I have found such 
a renewal in some Cribrilinidae and in Porina flabeUata d’Orb. 
M Op, cit. 
G. M. R, Levinsen, Om Fornyelsen af Ernæringsindividerne hos Hy- 
droiderne, Vidensk. Meddel, fra naturh. Forening, 1892, pag. 14. 
3) Paléontologie fran 9 aise, Terr. cret. Bryozoaires, PI. 699, fig. 2. 
