NORTH AMERICAN EARLY TERTIARY BRYOZOA. 



53 



(fig. 9, E). In certain species (see Membrendoeeium duplex] some of the zooecia 

 are without dietellae. 



FUNCTIONS OF REPRODUCTION. 



LARVA. 



The great obstacle in bryozoology is the lack of knowledge of the larval system, 

 for studies on this subject are really very incomplete. Moreover, any attempt at a 

 general classification is impossible at present, because each family is undoubtedly 

 characterized essentially by its larva. Nevertheless we are able to utilize with 

 success the studies on this subject made by Smitt in 1865, Barrois in 1877, and 

 Calvet in 1900. In our text figures we have reproduced illustrations of the larva 

 wherever known. 



FIG. 9. Septulae and dietellae. 



A. Uniporous septulae of Ilippopodina fegeensis Busk, 1884, X 40. 



B. Multiporous septulae or disk septulae of Cheilopora sincera Smitt, 1877, X 25. (A, B, after 

 Levinsen, 1909.) 



C. Hippodiplosia paUasiana Moll. 1803; a, multiporous septula, X 350; b, schematic lougitudi 

 nal section through a multiporous septula ; c, schematic longitudinal section through a dietella 

 (After Levinsen, 1909.) 



D. Dietellae of Callopora lineata Linnaeus, 1768. (After Norman, 1903.) 



E. Dietellae of Trypostega venusta Norman, 1864. obtained by abrasion of the frontal of a 

 specimen from the Vicksburgian at Byram. Mississippi. 



OVICELLS. 



The esres are transformed into embryos and into larvae within cavities of 



BO * 



incubation. These cavities, when they are visible, are called ovicells. 



Nonovicelled zooecia. A large number of species of Cheilostomata show no 

 ovicells and nothing on the exterior reveals their mode of reproduction. Some are 

 oviparous and expel their eggs by an intertentacular organ (Electrinidae) . Others 

 develop their embryos in the tentacular sheath ( Cyclostomata ) . There is quite an 

 important group in which the cavity is a membranous sac attached to the sub- 

 diaphragmatic region of the tentacular sheath ; often the female zooecia are identical 

 with the others (Lepralia cucullata Busk, 1852, Beniua ,,i<j,ll<m'-ti Busk, 1S50. 



