How does the digestive system of a hydra compare with that of an earthworm?
This is an interesting – if rather standard – exam question. Looked at from an evolutionary point of view it is clear that the gut structure present in the earthworm offers far more potential than the hydra’s simple ‘gutbucket’and has, (unlike the latter) been exploited along the length of the evolutionary path starting from the point after hydra. The questions that follow from this include how did the gut structure evolve, what competitive advantage does it offer and, most important of all, why.
