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BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 
tous] threads passing to the peculiar body, and the vitality of the colony will, both 
in times of full and diminished vigor, be increased by the avicularia; for the con- 
stant snapping of the mandibles often continues when the polypides are not extend- 
ing themselves out the zooecia, and, as before said, even when there are few or 
no polypides. Sections often show the avicularia in unchanged conditions, when 
the zooecia only contain hvstolysed remains of polypides.” (Waters, 1904.) 
The avicularia are not protective organs, as former authors believed; in fact, 
they are developed and much elongated in the most protected part of the zoarium. 
This phenomenon is of constant occurrence in the Cellepores. 
The avicularia develop very often in the place of the tremopores and areolae; 
the zoologists have figured many examples of them ; we ourselves have been able to 
observe such occurrences on Schizopodrella linea Lonsdale, 1845, and on Enoplo- 
stomella synthetica Canu and Bassler, 1917. 
There are three principal kinds of avicularia — articulated, frontal or immersed, 
and interzooecial. 
The articulated avicularia exist on the articulated zoaria ; they are often very 
complicated and quite perfected organisms (fig. 13, A). 
Frontal or immersed avicularia. — These are quite variable; it is always possible 
to distinguish the corneo-chitinous mandible, the calcified beak, the membranous 
frontal area, and a mandibular cavity. (Fig. 13, B.) These are quite small and 
simple, without pivot or denticle, hardly distinct from the areolae. 1 Others, on the 
contrary, are highly perfected. (Fig. 13, C.) The glands mentioned by Waters 
have unknown functions. 
Interzooecial avicularia. — There are ordinary zooecia deprived of polypide and 
containing only muscles. (Fig. 13, E.) Their variations are very important, for 
they express corresponding anatomical peculiarities. Their frontal is chitinous in 
the Malacostega (fig. 13, F), calcified in the Coilostega; in the latter case they 
constitute the onychocedlaria (figs. 13, G, H) of Jullien, and in the group of the 
Tubifera they form the reticulocellaria of Canu (fig. 13 I). They are straight and 
symmetrical if the polypide of the adjacent zooecium has its large retractor muscle 
placed at the middle of the base (fig. 13, H) ; they are unsymmetrical if the same 
muscle is attached laterally, as in the genus OnychoceUa (fig. 13, G). In the Asco- 
pliora the interzooecial avicularia occur chiefly in the family Adeonidae. Never- 
theless it is not rare to find some zooecia provided with a mandible ( Porella planu- 
lata , new species, M etroperiella grandipora , new species, etc.). (Fig. 13, J.) 
V ibracula. — The vibracula are het.erozooecia formed of a cavity with chitinous 
or calcareous walls and of a long cilium or seta. Their organization is identical 
with that of the avicularia; they differ only in the articulation of the seta (=whip 
or flagellum) and in the great length of the latter. 
“ The base of the asymmetrical seta of the vibracula is very complicated with 
a large number of curiously shaped protuberances, to some of which the muscles 
1 On the fossils it is often impossible to say if an observed small pore is a tremopore, an avicularium, a 
vibraculum, or a radicular pore. 
