There is no consensus among
researchers regarding what qualifies a
substance as a pheromone. While most
Line agree on a basic definition of pheromones
(5) as chemicals released by one individual
of a species which, when detected by
another individual of the same species,
elicit a specific behavioral or physiological
response, some researchers also specify
(10) that the response to pheromones must be
unconscious. In addition, the distinction
between pheromones and odorants-
chemicals that are consciously detected
as odors---can be blurry, and some
(15) researchers classify pheromones as a
type of odorant. Evidence that pheromone
responses may not involve conscious odor
perception comes from the finding that in
many species, pheromones are processed
(20) by the vomeronasal (or accessory olfactory)
system, which uses a special structure in
the nose, the vomeronasal organ (VNO),
to receive chemical signals. The neural
connections between the VNO and the
(25) brain are separate from those of the main
olfactory system, whose processing of
odorants triggers sensations of smell. But
while the VNO does process many animal
pheromone signals, not all animal phero-
(30) mones work through the VNO. Conversely,
not all chemical signals transmitted via the
VNO quality as pheromones. For example,
garter snakes detect a chemical signal from
earthworms-one of their favorite foods-via
(35) the VNO, and they use this signal to track
their prey.

The primary purpose of the passage
is to
A. compare and contrast the ways
in which the vomeronasal organ
and the main olfactory systern
process chemicals.
B. summarize the debate over the
role the vomeronasal organ
plays in odor perception
C. present some of the issues
involved in the debate over
what constitutes a pheromone
D. propose a new definition of
pheromones based on recent
research
E. argue that pheromones should be
classified as a type of odorant