Gonozooecia in the Adeonidae whose structure is still very imper- 
fectly known, we can distinguish the three following types: 
Autozooecia which contain a polypide and are provided with 
an orifice. i 
Heterozooecia which lack a polypide or possess only a feeble 
rudiment of it. On the contrary they are provided with a power- 
full muscular apparatus for the movement of the operculum which 
is modified in various ways. To this type belong the avicularium 
and the vibraculum. 
Kenozooecia which lack both a polypide and an orifice. To this 
type belong the partitions composing the connecting tubes, the ra- 
dical fibres, the stolons and stalks (Stirparia, Chlidonia), the sin- 
gular lateral chambers (loculi) of the Catenicellidae, the modified 
marginal zoocia in several species of Flustra, the small chambers 
forming the basal expansion in the colonies of BRetepora and the 
supporting tubes of many Cyclostomatous Bryozoa. 
The front wall. According to Harmer the calcified front 
wall in the Camarostega corresponds with the united overarching 
spines of the Acanthostega, the membranous opercular wall of which 
is represented by the floor of the compensation-sac, but at the 
same time this author admits that ,,the calcareous matter of Chei- 
lostomata is probably always covered by an ,,epitheca" limited by - 
å cuticle of chitine or other organic substance". If Harmer were 
right in his interpretation we should expect to find the overarching 
spines of a Cribrilina provided with a similar epitheca, but I have 
never been able to detect the slightest vestige of a membrane covering 
the spines, neither in Cribrilina nor in Membranipora, although such 
a membrane is very distinct in the calcified part of the front wall 
surrounding the area. According to my investigations the mem- 
brane named ,,epitheca" is the original membranous surface of the 
z00ecium, and the calcified front wall originates under this membrane 
in direct connection partly with the side-walls: partly with the 
proximal wall. While the front wall in most species of Flustra 
is represented only by a membrane extended within a calcified 
g 1% 
