NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
53 
(fig. 9, E). In certain species (see Membrendoecium 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 Hippopodina 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 pallasiana Moll, 1803; a, multiporous septula, X 350; 6, schematic longitudi- 
nal section through a multiporous septula ; c, schematic longitudinal section through a dietella 
(After Levinsen, 1909.) 
D. Dietellae of Callopora lineata Linnaeus, 176S. (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 eggs are transformed into embryos and into larvae within cavities of 
incubation. These cavities, when they are visible, are called ovicells. 
N onovicelled 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 (Cvclostomata) . 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 cumllata Busk, 1852, Beania mayellanica Busk, 1S50, 
