56 
BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 
The observations of Jullien appear to us more exact. In fact, almost always, 
the formation of the ovicell is identical with that of the frontal. There are, how- 
ever, some exceptions ( Smittina , Umbonula). Moreover, all the observations of 
Levinsen are explained rather well by the manifestations of the three calcareous 
deposits previously noted — olocyst, trcmocyst, and pleurocyst. In all of our studies 
we have not once found it necessary to have recourse to his theory. 
Passage of the eggs. — The eggs are formed in the general cavity, but they clo 
not develop there. They pass into the ovicell, where, by successive segmentation, 
they are transformed into embryos and into larvae. This passage is very delicate 
(fig. 11, A) ; it is assured by the tentacular sheath or by a sacciform expansion of the 
endocvst (fig. 11, B) ; it is protected by some arrangements as varied as remarkable 
and of which the principal are the following : 
1. The functioning of a special operculum to the ovicell (fig. 11, C). 
2. The functioning of the zooecial operculum itself, which closes the orifice 
of the ovicell either always or only during the passage and the incubation. The 
operculum is then strongly chitinized to serve for protection (fig. 11, D). 
3. The development by thickening of the walls of a peristomie into which the 
orifice of the ovicell opens (fig. 11, E). The aperture is deep and closed by a 
fragile operculum. The exterior orifice of the peristomie is the peristomice ; it is 
irregular and surrounded by the peristom.e. 
4. The obliquity of the apertura and the imbedding of the ovicell in the distal 
zooecium forms a very small chamber or locella sufficiently protected; moreover, 
the mucro, the labial appendages, and spines complete this little cell (fig. 11, F ). 
Fixation of the larva; Ancestrula. — -The larva of the cheilostomatous bryozoa 
after some hours of life in liberty becomes fixed on a substratum and then grows 
into the zoarium. The first zooecium is the ancestrula. In the Malacostega this 
ancestrula is analogous to the other zooecia, but smaller. In the Anasca there is 
more variety. More often the ancestrula is a small zooecium identical with the 
others. Frequently there are some interesting variations which have been studied 
by the zoologists. 
On fossils the ancestrula is very fragile and is very often broken. We have 
been able nevertheless to figure a score of specimens almost always identical with 
the zooecia. Only Puellina radiata Moll. 1803, Rhamphostomella simplex, new 
species, and Smittina puncturata , new species, have given membra niporoid or modi- 
fied ancestrulae. 
The larvae of the bryozoa are not fixed at hazard ; they chose their own sub- 
stratum, which is surprising. The Lunulariidae choose a grain of sand; others, 
shells and stones; others, marine algae; and still others live only on a special 
species of mollusca or bryozoa (symbiosis). The reader will find in the course of 
this monograph many interesting cases that we have noted. When these observa- 
tions are sufficient they will permit us to reconstruct the submarine depths and their 
biologic conditions. 
