Three Organisms: Hydra, Flatworm, and Earthworm

The Hydra, unlike other animals with an anus and rectum, uses the same opening for both taking in food and eliminating wastes.   Its intracellular and extracellular digestive processes are detailed in the drawing I have made.   It is the simplest of animals in the drawings, since it uses a contractile fibrils lining in its skin.   The cells lining in the Hydra can take in solid bits of food with the internal cavities.   Special cells of the hydra secrete enzymes into the central or digestive cavity, where they digest food.   The products of this extracellular digestion are absorbed by the body cells.   The central cavity of the Hydra has only one opening.   Materials cannot be digested.


The flatworm is more complex than the Hydra.   Its digestive cavity has only one opening.   A muscular organ in the flatworm called the pharynx takes in bits of solid food.   The food is digested in a branched digestive cavity, then absorbed by the body cells.   The pharynx extended through the mouth, lets out undigested food while letting in food too.   It uses a muscular pharynx to do this type of action.   The intestines are split into subdivisions for absorption of digested foods.


The earthworm uses a complex structure to eating foods.   Its system is an example of the complete digestive tube with two openings.   The mouth at one end, through which food is taken in, and the anus at the other end, through which wastes are eliminated.   The movement of food and undigested wastes becomes one-way traffic in complex animals with an opening at each end of the digestive tube.   The earthworm contains a pharynx that mixes the food with a moistening secretion and pushes it farther along the tube.   The earthworm's digestive tube has an enlargement called the crop where food is stored.   Food is moved from the crop into the gizzard in earthworms.   It also has an intestine where digestive enzymes are secreted by cells of the intestinal lining.


The above three organisms have comparing...