and the colony as a whole is withdrawn. In some
species so-called macrogonidia, or larger sexual individuals, are
developed alongside the usual ones. Fresh and salt water.

Zoothamnium elegans D'Udekem '64? Fig. 61.

The bodies are variable--peristomial border widely dilated, tapering
and attenuate posteriorly. The pedicle is slender, smooth, and
transparent, and branches sparsely at its distal extremity. There
are but few zooids (3 to 4). The ciliary disk projects conspicuously
beyond the peristomial border. The pharyngeal cleft is very distinct
and extends beyond center of body. Length of body 80 mu.

[Illustration: Fig. 61.--_Zoothamnium elegans_.]

Genus COTHURNIA (Ehr. '31) Clap. & Lach. '58.

Colorless forms of medium size-in some cases they may be green
by Zoochlorella. The general structure is similar to that of
_Vorticella_, but the individuals are elongate and occupy houses. The
macronucleus is invariably long and band-form. The distinguishing
character is the colorless or brownish lorica of quite variable form
but always attached. These houses may be finger-formed, with widened
center, or widened mouth, or constricted mouth, and the like.
Ring-formed swellings are frequently developed. Sometimes the mouth
becomes twisted and the lorica is therefore bilateral. The houses
are attached either directly to some foreign object or by means of
a short stalk. The animals are similarly fastened to the lorica,
sometimes directly, sometimes by means of a short stalk. When they
contract they draw back to the bottom of the lorica; when expanded
they usually stretch out of the mouth opening. In some forms there
is an operculum, by means of which the opening of the shell can be
closed when the animal is retracted. Fresh and salt water.

The number of species of _Cothurnia_ has become so great that the
difficulty in placing forms is almost sufficient to discourage the
systematist; as Buetschli well remarks, the variations in the theca
have been made the basis of new species so many times that the
genus is almost as confused as _Difflugia_ among the rhizopods or
_Campanularia_ among the hydroids. The length of cup, of stalk,
the presence of annulations on stalk or cup, etc., have given rise
to many specific names, the majority of which I believe can be
discarded. According to such differentials the same branch of an alga
holding a hundred specimens of _Cothurnia crystallina_ yield 10 or 12
species, whereas they