On 4 Nov 2009 07:29:48 -0800, TomS <TomS_mem...@newsguy.com> wrote:

Tear ducts are found in pretty much all tetrapods.  But there really
is a question of what they are supposed to do.  Carrying off excess
tears is not much use -- there is no problem in just having the fluid
run out of the eye.  And there is no particular value in shunting it
into the nasal cavity.  So the problem is why it should be there at
all.

Willem Hilllenius, the chair of the Biology department at the College
at Charleston, is interested in the Harderian gland in amphibians.
This is a specialized gland in the eye orbit of many tetrapods and
Hillenius (with Susan Rehorek of Slippery Rock University) speculates
that its secretions might be closely connected with the vomeronasal
(Jacobson's) organ, a sensory structure in the nasal passages.  They
have a paper in J. Herpetology

  WJ Hillenius, LK Watrobski, and SJ Rehorek
  Passage of Tear Duct Fluids through the Nasal
     Cavity of Frogs
  J. Herpetology 35(4):701-704 ( 2001)
  http://www.jstor.org/pss/1565918

showing that the lacrimal duct transmits fluid from the Harderian
gland to the vomeronasal organ. Thus the secretions of the gland could
be used to bind to and carry scents, especially pheromones,  picked up
from the air (or water in the case of amphibian animals) to the
sensory structure.  The Harderian gland - tear duct - vomeronasal
organ connection seems to be shared by, for example, frogs and
caecilians (among the amphibians) and snakes (among the former
Reptiles) and so was probably an important factor in early tetrapod
evolution.  Using the large, moist exposed surface of the eye to
collect scents is probably as effective as the snake habit of flicking
out its tongue to capture odors for presentation to the vomeronasal
organ.