DEVELOPMENT OF THE POLYZOA. 145, 
lar interest. The free-swimming ciliated larva is provided 
with a bivalve shell, and was originally described as a La- 
mellibranch larva under the name of Cyphonautes. 
Schneider discovered that it was a young Membranipora. 
Barrois, who has traced its complete history, states that its 
metamorphosis is fundamentally like that of the other ma- 
rine Polyzoa. Flustrella hispida passes through a similar 
Cyphonautes stage. 
In Loxosoma young resembling the adult bud out like 
polyps. Nitsche does not regard this budding process as an 
alternation of generations, but states that in Polyzoa of the 
family of Vesiculariide, this may occur, as in the latter 
some cystids form the stem, and others (the zowcia) produce 
the eggs. Most fresh-water Polyzoa reproduce by the devel- 
opment of winter buds or eggs surrounded by a horny case, 
and developing from the funiculus. 
To recapitulate : the Polyzoa increase (a) by budding ; (4) 
by normal (summer) eggs, and by producing statodlasts, or 
winter eggs. In reproducing from summer eggs, the young 
pass successively through a morula, blastula, gastrula and 
trochosphere stage before attaining maturity. 
The most aberrant Polyzoan is Rhabdopleura mirabilis Sars, 
which occurs in from 100 to 300 fathoms on the coast of 
Norway. It differs from other forms by the want of an en- 
docyst or mantle, whence it moves up and down in its cell, 
without being attached to the opening, the muscles usually 
present being wanting, the cord by which it is attached to 
the bottom of its long, slender tubular cell being contractile. 
The lophophore is much like that of the fresh-water Poly- 
zoans, consisting of two long arms, bearing two rows of 
slender tentacles. The epistome is represented by a large 
round disk. 
The marine Polyzoa occur at great depths, and a few species 
are cosmopolitan ; the type is very persistent, and occurs 
in the oldest Silurian strata, the earliest forms being very 
similar to their living descendants, 
