Thanks for all the input. I don't think I'm expressing myself well, however. I'm not saying that I don't see differences between bats. That's absurd. If you show me a picture of an animal that is a bat, I would probably identify the animal correctly as being a bat. And so would the rest of us laymen, as you put it.

And if you were to ask me to delineate superficial or easily recognizable differences between bat species, I could do that, too, as could other people who used their eyes with discernment.

So I'm not idiotically saying that all bats look identical. I'm saying that bats can appear to be similar--oh, lucky for us who want to go bat chasing--and that some bats appear to be more similar in appearance than do some breeds dogs.

I took a look at some photographs of bat skeletons, in fact, and those skeletons were remarkably similar in many ways to human skeletons. They were also very different from human skeletons. The similarities were equally interesting to think about as the differences.

My whole point here that I'm having great difficulty in expressing is this:

What is the defining feature that distinguishes species from breeds? I think probably Faldage has hit upon it--that generally, at least, species are so distinct that the likelihood of breeding between two separate species is low, although I do understand that in some cases species can cross, as in the lion/tiger cases you pointed out. I suppose if you were to leave certain bat species in isolation for a while there would be certain ones that would breed with each other out of boredom or anxiety.

Would it be correct to say that species generally breed within each species and that breeds of similar species of animals readily breed with other breeds of that same species of animal?

Would it be correct to say that species most likely breed within the species because of geographical proximity, dietary habits (as of troy mentioned), group dynamics, and diurnal and nocturnal proclivities?

And would it be correct to say, based on what you have written above, that breeding across species has been well-documented, but it is rare and will often produce infertile offspring, though not always?

And, finally, is it to correct to say that superficially, at least, some breeds appear to have more startling differences in appearance than some similar species (i.e., some breeds of dogs look more different from each other than some species of bats)? [I could probably choose two species of dogs that appear to be very different, such as, say, a Newfoundland and a dachshund, and two very similar bat species, such as the hairy-legged vampire bat and the common vampire bat:

http://www.scz.org/animals/b/vampire.html

http://www.batcon.org/batsmag/v11n4-14.html

...not to mention the Seminole bat that looks a lot like the vampire bats above.

*And I'm not saying at all that I can't tell the differences between these bats. I'm just saying that some breeds of dogs have more superficial appearance differences than some superficial appearance differences of some species of bats. Distinctive feature identification is a personal obsession of mine.