Fromentel described a fresh-water form of this genus with a caudal
appendage. The body is pyriform, broadly truncate on the anterior
end, in the middle of which rises a papilliform process (Schnabel).
On this process is a heap of pigment granules, which, however, are
not constant. A ring of long cirri surround the anterior end and pass
into the peristome, and from the left edge of this line of cirri a
large adoral zone continues down to the mouth. The peristome is
elongate and sac-form, and the mouth lies at the posterior extremity.
With the exception of a caudal filament there are no other motile
organs; this is about half as long as the body, structureless,
hyaline, and sharply pointed. It splits up into a bundle of fine
fibers upon treatment with caustic potash (c). The cirri emerge from
minute hollows in the edge of the anterior border. The cortical
plasm contains peculiar rod-like bodies, which look more like lines
or markings than like rods or trichocysts. The nucleus is large,
spherical, and placed in the center of the body. The contractile
vacuole is posterior.

Length without appendage is about 35µ; greatest diameter 15 to 18µ.
In decaying vegetable matter. Common.


[Illustration: Fig. 46.--_Strombidium caudatum_.]


Although Fromentel's species is incompletely described, it is very
evident that the organism corresponds fairly well with the Woods Hole
variety. His was a fresh-water type; this is marine, but the caudal
filament and the contractile vacuole are similar. Certainly in this
case the organism can not be regarded as a Vorticella broken off its