Worm Dissection

     Unfortunately I was unable to participate in the earthworm digestion. Seeing the parts of a worm in actuality,rather than textbook diagrams would have helped to increase my understanding of an earthworm anatomy.
     The main purpose of this dissection was to achieve a better understanding of an earthworm's organs and also the systems which it has. Such as the circulatory system, the digestive system, the respiratory system, the excretory system and the nervous system. The lab was an opportunity to observe the internal and external structures of an earthworm. After this lab we would be able to name and identify the organs of a earthworm.
      We had just finished the chapter on annelids. Thus doing the lab was a great way to incorporate the textbook learning with a hands on dissection. The lab began with a identifying the dorsal and ventral sides of the worm. We also noticed the clitellum which is used in the reproductive system of earthworms. We then later looked at the five aortic arches (hearts) and find the nerve which are connected to the rest of its body. The next part of the digestion was the digestive tract. We took a look at the pharynx, esophagus, crop, gizzard and intestine. For the excretory system we found the nephridia that are found in each segment twice. We identified ovaries and testes for the reproductive systems of the earthworm
  By doing this lab we can take our level of the earthworm's anatomy a step farther. It has helped us understand where and why organs are located where they are.

  Discussion Questions:

 

1. The aortic arches are the organs which pump blood throughout the earthworm's body. They are also know as hearts, and a earthworm has 5. The fluid travels through the ventral blood vessels to capillary beds. The dorsal blood vessels is where the fluids collect and are transported back to the aortic arches.

2. The digestive tract of an earthworm consists of the pharynx, esophagus  crop, gizzard and intestine. The mouth is the first part of an earthworm's digestive tract. Then it goes into the pharynx, which pumps pumps the food into the esophagus (tube between pharynx and crop). The crop stores the food temporarily. The gizzard then grounds up the mixture and in the intestine digestion and absorption occur. 

3. The nerve collar consists of galngia above and below the pharynx. (Ganglia are masses of tissues with many nerve cells)The ganglia above the pharynx serve as the brain. There is a long ventral cord which has ganglion connected to each organ. 

4. The nephridia are the parts of the earthworm which are included in the excretory system. Nephridia are simple tube-shaped excretory organs which eliminate wastes caused from cellular metabolism. They remove waste from body fluids and carry it outside. A pair of nephridia can be found in each body segment.

5. You can know if an earthworm eats soil by looking at what  is in the digestive tract. You can also look at an earthworm's waste products to determine whether or not it eats soil.

6. The setae make the earthworm well adapted to it's environment because they help them crawl and anchor themselves firmly in their burrows. They also help the worm grip the soil making it difficult for it's predator to pull the earthworm out. 

7. The earthworm's digestive system is adapted for extracting relatively small amounts of food from large amounts of ingested soil because of it's gizzard. The gizzard is an organ which is used to churn food (ground into smaller pieces). 

8. Beyond segment 32 is the clitellum. It is located from segment 32-37.  The rest of the posterior end has the intestine of the worm and the anus. The intestine has solid and liquid substances which is the food of an earthworm. 

9. Earthworms are hermaphrodites which undergo fertilization. An individual worm produces both eggs, in the ovary, and sperm in the testes. However it does not fertilize itself. When an earthworm undergoes they reproduction, the worms pair up and attach themselves together. The clitellum secrets a mucus into where eggs and sperms are released. The eggs are released by the female genital pores and the sperm from the male genital pores. After the egg and sperm are released the mucus slips off. Fertilization then takes place outside the body, but with the protection of the mucus ring. This mucus turns into the cocoon.