<span>This is the condition under which he would classify them as belonging to different species - the two salamanders cannot mate to produce a fertile offspring. If these two lizards belonged to the same species, they would normally be able to breed and give birth to a fertile new "child." However, given that they are not of the same species, they cannot do such a thing, which is why this scientist classified them that way.</span>
The two differences you see when comparing the four chambers of the heart is that the arteries have a thicker wall and veins have thin walls and that the arteries carry oxygenated blood away from the heart which means they get more pressure than veins.
