Introduction to some aquatic protozoa in Essex
for locomotion and is very easy to observe while the other sits within the reservoir and does not
appear to do anything. The photograph below was taken with x40 phase contrast objective with a
total magnification of x500 using a Leitz Orthoplan. The halo that appears around objects taken
with this type of contrast equipment is quite normal. The film used was 160 Tungsten calibrated for
3200 °K
Figure 5. Euglena acus under x500 magnification in phase contrast lighting © Steve Durr
Photography with a microscope
One of the most interesting things about developing and printing your own photographic images is
that you get to see the results coming to fruition before your eyes. Using black and white photography
at the microscope does necessitate the use of filters for improving contrast. Below are some
photographs (Figures 6a and b) that I took of the common Stentor polymorphns, which can sometimes
appear green due to the large amounts of Chlorella that it manages to ingest. Both these photographs
were taken with technical pan rated at 64 ISO and developed in technidol.
This protist is quite large and has a voracious appetite for bacteria and almost anything else that it
can manage to swallow. Stentor belongs to the spirotrichs and has cilia all over the body. It is
shaped like a trumpet when fully extended but will contract very rapidly when disturbed. Stentor can
vary in colour from grey to green depending upon what it has been feeding on. The row of cilia,
which can be seen at the anterior end of the organism, is called the adoral zone of membranes. These
membranes of cilia create a vortex in which any organisms that are caught in their influence are
sucked into the cytostomc (mouth area). When using differential interference contrast (DIC) lighting
the macronucleus can be seen like a string of beads, depending upon which species is being observed.
Stentor will usually be found attached to the substratum by its holdfast and, therefore, can easily be
observed and also photographed.
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Essex Naturalist (New Series) 18 (2001)