NORTH AMERICAN EARLY TERTIARY BRYOZOA. 



57 



The transformation of the larva into the ancestrula has been the subject of the 

 histological works of Barrois, 1877, and of Levinsen, 1900. The zoarial budding 

 lias been the subject of works of Haddon, 1883; Davenport. 1891; Calvet, 1900; 

 Waters, 1906, etc. 



FIG. 11. Passage of the eggs. 



A. Lepralia martyi Joliet, 1S77. a. Egg commencing to approach the entrance of the ovicell. 

 b. The same, some hours after and in which the egg is already strongly engaged in the passage 

 of the ovicell. (After Joliet, 1877.) 



B. Schizopodrella (Schizoporella)nivea Busk, 1884, X 50. A sac-like structure (sc) is shown 

 at the base of each ovicell (oc), but of the numerous muscles in this sac only about half of 

 those in focus are drawn. It seems that the ovum (ov) passes into this sac which is then rup- 

 tured (r) and the ovum is pressed forward into the ovicell, where it segments. The small 

 oral glands (gl) are shown. .Em 6= embryo. (After Waters, 1913.) 



C. Schizopodrella (Schizoporella) unicornis .Johnston, 1S47. Operculuin of the ovicell. (After 

 Levinsen, 1909.) It is probable that this figure is only a schematic one after a longitudinal 

 section on the order of figure B. cm, covering membrane; or, cryptocyst; ekto, ectocyst; endo, 

 endocyst; oo, ooecial operculum; op, operculum ; v, vestihulnm. 



D. Micropora coriacea Esper, 1797, X 40. The operculum closing the ovicell protects the 

 passage of the eggs. (After Levinsen, 1909.) 



E. Gastropella ventricosa Canu and Bassler, 1917. Sketch showing development of a peris- 

 tomie above the ovicell. 



op, apertura ; asc, ascopore; ol, olocyst; ov, ovicell; pi, peristomie; pic, peristomice; pi, pillar; 

 z, zooecium. 



F. Section through ovicell showing the locella protecting the passage of the eggs. 

 loc, locella ; op, operculum ; ov, ovicell ; zd, distal zooecium ; zp, proximal zooecium. 



HYDROSTATIC FUNCTIONS. 



Zooecial hydrostatic relations. The discovery of the zooecial hydrostatic sys- 

 tem of the Cheilostomata was made by Jullien in 1888. It explained the greater 



1 1888. Jullien, Sur la sortie et la rentre'e du Polypide dans les zooecies chez les Br.vozoaires Cheilos- 

 tomiens monodermigs, Bulletin Socigte Zoologique France, vol. 13, pp. 67, 68. 



