NORTH -AMERICAN EARLY TERTIARY BRYOZOA. 



157 



eryptocyst and the ectocyst is the hypostege or hydrostatic zooccial chamber. \Ve 

 do not yet know whether the hypostege contains sea water as in the compensation 

 sack of other Cheilostomata or was tilled with the fluid of the general body 



cavity. 



Fio. 38. Genus Amylrililestrum Gray, 184S. 



A-E. Aniiiltiblextrum fleitiingii Busk. 1825. A. Zooecia, X 50 (after Hincks, 1880). B. 

 Sketch showing dietelle (after Norman. I'.MI:!. ) C. Section in the ovicell (after Calvet, 30(10). 



"/), operculurn. 



ns, zooecial orifice. 



si, internal sack. 



foi, inferior ovicell vesicle. 



cos, superior ovicell vesicle. 



bi, inferior bryozooid. 



bs, superior bryozooid. 



co, coronna. 



r. embryo. 



iiiidl, dilator muscle of incubation cavity. 



D. Avicularian mandible, X 85 and X 250 ^fter 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. ecto, oral ectoderm. 



< . mantle. one, central nervous organ of the embryo. 



(I, tampon of the internal sac: Pise, sub-ectodermal nerve plexus. 



epm, mesoderm thickening. spa, palial furrow. 



F. Amphiblestrum tri folium Wood, 1850. Sketch showing dietellae i after Norman, 19031. 



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. 



