The first animal dissected was the earthworm, which has a fairly basic digestive system. Food is ingested by the earthworm through the mouth, and then it passes through the small buccal cavity and the pharynx. From there, the food moved to the esophagus and then to the crop, where the food is moistened and stored for a short time. After leaving the crop, the food travels to the gizzard, which grinds the food before it enters the intestine. Nutrient absorption takes place in the intestine, and finally wastes are expelled at the anus.

The digestive system of the mussel is slightly more complicated than that of the earthworm, due to the addition of the stomach and digestive glands. Food enters the mussel through the mouth, and then travels along a tube to the stomach. In the stomach, enzymes produced by the digestive gland are released to break down digestible material. In addition, the stomac

Having described the digestive systems for each of the organisms dissected this semester, now we will discuss the observed changes from primitive to more advanced. It is during the dissection of the mussel that we observe the first change in the digestive system. The mussel has a stomach, which the earthworm does not have. This addition of the stomach allows the mussel to break down digestible material via enzymes which are produced by the digestive gland. The next change that occurs is in the sectioning of the stomach in the crawfish. This is different than the mussel or earthworm, and may reflect the different foods consumed. It may be necessary for the stomach to be sectioned. The starfish has a system similar to the crawfish, with the major difference being the mobility of the cardiac stomach. As discussed above, the starfish pushes out it's cardiac stomach in order to engulf it's prey. Once again, the change we see here from primitive to more advanced seems to be necessary, in order for the starfish to consume the food necessary to survive.

Having dissected each of these organisms and discussed the observed changes, I have come to the conclusion that the change in digestive systems from primitive to more advanced is necessary to facilitate increased consumption. It is also clear to see that each of these changes along the way greatly aid in the efficiency of the digestive system. The stomach allows for the break down of digestible material. The sectioning of the stomach allows for break down of food into smaller particles and added nutrient absorption. The addition of digestive glands allows for the secretion of digestive enzymes. The liver produces bile, which aids in the digestion of fats, while the pancreas secretes additional digestive enzymes into the i

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