Self And The Phenomenon Of Life: A Biologist Examines Life From Molecules To Humanity

The Microbial Self 85

“9x6” b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity

4.2.2 Stentor avoidance behavior

Stentors are unicellular aquatic organisms measuring about 1 mm in
length. They have a trumpet-shaped body and normally attach their nar-
row end to the vegetative debris in a pond. The open end is the oral
cavity, which actively sucks in food by means of a vortex created by a row
of cilia surrounding the cavity. The food passes into an oral pouch then
into the gullet before turning into food vacuoles. The stentor will stay
in one place to feed until food is deprived, or until the condition is no
longer favorable, whereupon it swims away to another location. Stentors
exhibit a high degree of food selection. At the oral pouch living objects
are taken in, whereas indigestible particles are rejected. Among living
organisms some species (such as euglena) are preferred to others (such
as chilomonas) as food.
The most elaborate behavior of stentors is one of avoidance of a
noxious stimulus (Fig. 4.2), as documented by H. S. Jennings.^11 Jen-
nings did an experiment wherein a cloud of indigestible particle such as

Fig. 4.2. A stentor responding to carmine particles. Letters indicate sequence of
events. See text for details. [See Note 12; permission Elsevier Books.]