NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
157 
cryptocyst and the ectocyst is the hypostege or hydrostatic zooecial chamber. We 
do not yet know whether the hypostege contains sea water as in the compensation 
sack of other Cheilostomata or was filled with the fluid of the general body 
cavity. 
Fig. 38. — Genus Amphiblestrum Gray, 181S. 
A-E. Amphiblestrum flemmgii Busk, 1825. A. Zooecia, X 50 (after Hinclcs, 1880). B. 
Sketch showing dietelle (after Norman, 1903.) C. Section in the ovicell (after Calvet, 1900). 
hi, inferior bryozooid. op, operculum. 
bs, superior bryozooid. oz, zooecial orifice, 
co, comma. si, internal sack, 
e, embryo. cot, inferior ovicell vesicle. 
mud, dilator muscle of incubation cavity. cos, superior ovicell vesicle. 
D. Avicularian mandible, X 85 and X 250 i after Waters, 1885). 
E. Meridian section following a plane perpendicular to the median sagittal plane in an 
embryo almost completely developed (after Calvet, 1900). 
b, cellules of the upper vesicular collar. 
c, mantle. 
cl, tampon of the internal sac ; 
enrn, mesoderm thickening. 
F. Amphiblestrum trifolium Wood, 1850. 
ecto, oral ectoderm. 
one, central nervous organ of the embryo. 
pfse, sub-ectodermal nerve plexus. 
spa, palial furrow. 
Sketch showing dietellae ( after Norman, 1903). 
This organization is therefore identical with that of the Electrinidae, of the 
other Membraniporae, of the Flustridae, etc. The only difference is that the 
cryptocyst, being partially calcified, can be observed more easily. One consequence 
of this calcification is that the parietal muscles are observable only in the distal 
part of the zooecia. 
