DEVELOPMENT OF THE POLYZOA. 143 
Certain branching marine forms are provided with organs 
like birds’ heads, Sninted on astalk and called avicularia, with 
a movable jaw-like appendage, which keeps up an incessant 
snapping. Beside the avicularia, there are, asin Scrupo- 
cellaria, long bristle-like appendages to the cells, called 
vibracula. 
There are no organs of special sense in the Polyzoa, unless 
the epistome may be 1egarded as an organ of sense, and the 
nervous system consists of a single rounded ganglion (F’rede- 
ricella), or, as in Plumatella, a double ganglion, situated be- 
tween the mouth and vent, from which one set of nerves are 
distributed to the epistome, lophophore, tentacles, and evagi- 
nable endocyst, and another set to the various parts of the ali- 
mentary canal. A so-called colonial nervous system is sup- 
posed to exist in the Polyzoa, as when the ccencecium in some 
forms is touched all the polypides become alarmed, which 
indicates that aset of nerves connect the different polypides, 
though no such nerves have yet been discovered. The 
fresh-water Polyzoa are not sensitive to light, nor to noises, 
only to agitation of the water in which they dwell. 
All the Polyzoa are hermaphrodite, the ovary and male 
glands residing in the same cystid, the testis being situated 
near the bottom and attached to the funiculus, while the 
ovary is attached to the walls of the upper part of the cell. 
Allman regards the polypide and eystid as separate indi- 
viduals. The singular genus Lozosoma is like the polypide 
of an ordinary Polyzoan, but does not live in a cell (cystid). 
On the other hand, we know of no cystids which are with- 
out a polypide. Remembering that the cystids stand in the 
same relation to the polypides as the hydroids to the medusa, 
as Nitsche insists, we may regard the polypides as secondary 
individuals, produced by budding from the cystids. The 
large masses of cells forming the moss-animal, which is thus 
a compound animal, like a coral stock, arises by budding out 
from a primary cell. The budding process begins in the 
endocyst, or inner of the double walle of the body of the 
eystid, according to Nitsche, but according to an earlier 
Swedish observer, F. A. Smitt, from certain fat bodies float- 
ing in the cystid. 
