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, U-mbomila). Moreover, all the observations of 

 Levinsen are explained rather well by the manifestations of the three calcareous 

 deposits previously noted olocyst, tremocyst, 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 do 

 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, -4) ; it is assured by the tentacular sheath or by a sacciform expansion of the 

 endocyst (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 peristoimce; it is 

 irregular and surrounded by the peristom.e. 



4. The obliquity of the apertura and the imbedding of the ovicell in the distal 

 zobecium forms a very small chamber or loc.ella. 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 membraniporoid 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. 



