Bulletin - United States National Museum - Smithsonian Institution

8 BULLETIN 9C, UNITED STATES NATIONAL MUSEUM.
therefore in the study of the morphological variations of the organs
we now substitute that of their physiologic functions. Our studies
are therefore always directed toward the discovery of functions
which modify the skeletal form.
Family.—All the species which have the same larval form have
the same lineage and belong necessarily to the same family; there-
fore the family is characterized by the larval system. The ovicell
in which the larva developes is necessarily in rapport with it, and
a Ivnowledge of its structure gives the essential characters for readily
interpreting the j)hysiological purpose of the morphological and
skeletal variations.
Genus.—A really natural genus differs from another genus only
in possessing a different function and in the different form of any
skeletal part. The essential functions common to all bryozoa with-
out exception are:
1. Passage of eggs and escape of the larvae (=rapport of the
operculum and the ovicell).
2. Hydrostatic system and extrusion of the polypide (=:form of
the aperture and rapport of the operculum with the compensatrix).
3. Calcification and chitinization (=nature of the skeleton and
of the frontal considered as immediate deposits of the endocyst).
We have rigorously followed this principle in the establishment
of our new genera and we have also modified the diagnoses of the
described natural genera which were often incomplete.
The function of the avicularia and of the onychocellaria is not
known but it can not be common to all bryozoa because many species
are deprived of these structures; these structures therefore can not
furnish good generic characters. Nevertheless there are some groups
in which their presence appears to be absolutely indispensable to the
life of the zoarium and we have therefore considered them sometimes
in our generic diagnoses.
The general classification of the Bryozoa showing the larger sub-
divisions of the Cheilostomata is printed below for convenience of
reference.
Class. Subclass. Order. Suborder. Division.
fCtenostomata.
Cyclostoinata.
Trepostomata.
Gymnolaomata. J Cryptostoinata.
Bryozoa. [Malaco.stejra.
(Anasca. J Coilostega.
Phylactolaeruata.
Ascopliora.
[Pseiulostef^a.