in the family characteristics. The chief character is the attachment
of the posterior end by means of a single, longer or shorter, stalk,
which contains a highly contractile thread easily distinguished
in the living animal. Another character is the absence of colony
formation. Contractile vacuole, single or double, usually connected
with a sac-like reservoir. The macronucleus is invariably long and
band-formed, with attached micronucleus. Fresh and salt water.

So many species of _Vorticella_ have been described that the task of
collecting data and of arranging the synonyms is extremely irksome
and difficult. Stokes enumerates 66 species, inhabiting fresh and
salt water, and several other new species have been added since his
work. I am impressed with the fact that new species have been created
without proper regard for the manifold variations which nearly all
of the _Ciliata_ show, and I believe the 66 species might be safely
reduced to 12 or 15.


Vorticella patellina Müller. Fig. 59.

Body campanulate, widest at anterior border, from which it tapers
directly to the pedicle. The diameter of the peristome is a little
larger than the length of the body. The ciliary disk is but little
elevated. The cuticle is not striated and the body plasm is quite
transparent. Length 52µ.


[Illustration: Fig. 59.--_Vorticella patellina_.]