bristle-like. I was unable to find any cilia in the
peristome. One long caudal bristle, one-quarter of the length of the
body, trails out behind. The macronucleus is spheroidal and placed
near the center of the body; a conspicuous micronucleus lies near it.
A row of contractile vacuoles extends from the posterior end. I have
seen as many as six of nearly equal size and one or two smaller ones.
The intervals of contraction are quite long. Length 70 to 75 mu;
greatest diameter 10 to 12 mu.

_L. infusionum_ resembles _L. elongatus_ in its general form and in
its mode of life, for it excavates a retreat in zoogloea masses and
lies there for considerable periods perfectly quiet. It differs
from _L. elongatus_ and from _L. velifer_ (probably the same as _L.
elongatus_ of Claparede & Lachmann) in the presence of the caudal
bristle, in the absence of annular markings, number of contractile
vacuoles, and in the slightly smaller size. It resembles _Lembus
verminus_ (Mueller) as described by Kent (_Proboscella vermina_), and
_L. intermedius_ as described by Gourret & Roeser (_Lembus verminus_
syn.)in the absence of annular markings and in the presence of a
caudal bristle. It differs from the former, however, in the absence
of a tentacle-like process, and from both in the absence of a double
nucleus and in the presence of many vacuoles. These features are so
characteristic of all the specimens examined that I have concluded,
somewhat reluctantly, to give it a specific name. It is common in old
infusions of algae, especially after decomposition is well advanced.
Its food consists of bacteria.

[Illustration: Fig. 42.--_Lembus infusionum_.]

Lembus pusillus Quennerstedt 1869. Fig. 43.

Synonym: _L. subulatus_ Kent 81.

This species is much smaller than the preceding, and might easily
be mistaken for _Uronema marina_. It is subcylindrical in form, the
anterior end bluntly pointed, the posterior end rounded. The oral
apparatus is quite different from _Uronema_. The mouth, as in the
preceding species, is at the end of a long peristomial groove
extending from the anterior end to the middle of the body. The edges
of the peristome bear undulating membranes as in _L. infusionum_.
Like the latter, there is one caudal bristle, but unlike it there is
only one posterior contractile vacuole, while the endoplasm is filled
with large granules or food balls. The cuticle is distinctly striated
with longitudinal markings, and the cilia ar