Q. What are some evolutionary advantages of animals with complete digestive tube?

The complete digestive tube permits animals to continuously feed themselves without waiting for residuals to be eliminated before beginning the digestion of new foods, in this way the absorption of larger amount of nutrients is possible and therefore more and bigger complex species can develop. Digestive tubes with two openings also make digestion more efficient since they provide different sites with different chemical and physical conditions (stomach, mouth, bowels) for the action of different complementary digestive enzymatic systems.