 By going on to note that as many as have blood have a heart, he implicitly is warning the reader about a potential false inference one might draw from the examples so far: that all blooded animals have a lung. He mentions fish as an example of blooded animals without a lung, but immediately identifies the relevant differentia: ‘those blooded animals that have gills do not have these organs [the lung and its associated parts]’. He is careful not to restrict the universal to a kind—the relevant correlation is with gills, in whichever animals they might be found.