Re: Amphibians

Ok, let's slow down for a minute.

Now--
Class Amphibia (real-world amphibians) is a very ancient group of animals,
predating all other vertebrates except fish.  In their hundreds of millions
of years of existance, they have evolved in a number of different ways,
including breathing.
Ancestral adult amphibians possessed two means of respiration--their lungs
and a secondary system in their wet skins.  Oxygen and CO2 were exchanged in
both places, where present.  Ancestral larval amphibians were restricted to
aquatic environments and exchanged oxygen and CO2 primarily through gills--I
would assume their skin was also gas-permeable but don't know for certain.
    Modern amphibians are an intriguing mixture of systems.
Some--particularly frogs--have retained the ancient set up.  As larvae
(tadpoles), they exchange gases with gills.  As adults, most rely on their
lungs and their skin, although I am not entirely sure about some of the
purely aquatic species.  Toads respire as frogs, although their skin may not
be permeable.  Salamanders are far more diverse.  Some terrestrial species do
not have lungs at all and respire only through their skin.  Some retain their
larval stage into adulthood and respire with gills.  Some use lungs and skin.
 Caecillians I'm not sure about; I recall the ancestral burrowing form has
lungs, but I'm not sure about the aquatic species.

Rian A. McMurtry
B.S., Zoology
Attorney at Law