To me, the idea of a "species" is pretty irrelevant. I think the term "species", when used in the context of seperating one kind of animal from another, is pretty much a man-made division. Closely related animals can and do interbreed. If we try and breed between animals that differ further, then the chances of a successful outcome get less, until the two kinds of animal are too different to enable a successful pregnancy. I view the animal kindom more as a spectrum of more or less different animal designs, their likelyhood of interbreeding dependant upon the extent of the matching of their blueprints. The idea of seperate "species" might be useful for categorising the animal (and plant) kingdom, but as a concept gets in the way of our thinking regarding hybridising, and could be a barrier to our imagination when it comes to creating new kinds of creature.