How to Dissect an Earthworm
Earthworms are an important part of our ecosystem. They build tunnels and make the Earth's soil rich so that plant life can grow to its fullest potential. As a result, many people are interested in dissecting earthworms to learn more about how they are composed. Whether you're dissecting an earthworm on your own time or it's part of a biology class, this article will show you how to to dissect, step by step, so that you can observe the earthworm's organs and various segments.
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Things You'll Need
- Magnifying glass
- Dissecting tray
- Dissection pins
- Forceps
- Dissecting scissors
Instructions
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Observe the Earthworm's External Anatomy
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1
Locate the front end of the earthworm (called the anterior). Do this by finding the small, fleshy bump located over its mouth. This fleshy bump is called the prostomium. Also locate the back (called the posterior) part of the earthworm. The posterior has a small hole, which is the anus.
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2
Look for the part of the earthworm that is both thicker and smoother than the rest of the body. This section is near the anterior part of the earthworm and is called the clitellum. It contains reproductive organs.
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3
Observe for the many small pores on the earthworm with a magnifying glass. These pores are how the earthworm excretes liquid waste. The larger pores that you see are referred to as "genital pores" and are a vital part of the reproduction process.
Observe the Earthworms Internal Anatomy
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Place the earthworm on your dissecting tray to prepare for dissection. Its dorsal side (the darker side) should face up. Take your dissection pins and secure each end onto your dissecting tray. To do this, place the pins on either side of the earthworm to keep it from moving around. Do not puncture the earthworm.
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5
Relocate the clitellum and gently lift the area of the skin that is one inch below the clitellum with a pair of forceps. Cut an opening with your dissecting scissors and then place the scissors in the opening. Cut a line from this point all the way up to the earthworm's mouth. Cut slowly and carefully to avoid cutting the organs you'll observe later.
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6
Pull the two skin flaps apart from one another and pin them onto the tray. This will give you the best visual access to the earthworm's internal organs. If the skin does not fold back, then you did not cut deep enough. Simply cut along the line again to loosen the skin.
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Observe the internal organs. You will notice a lightly colored organ, the pharynx, that is located inside the mouth. Behind that organ, you will see five darkly colored "loops" that are wrapped around the esophagus. These loops are blood vessels that are referred to as the earthworm's aortic arches/hearts. Along the esophagus, you will also locate an organ called the "crop." This is where the earthworm temporarily stores its food.
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8
Look for a long, tube-like organ that stems from the earthworm's gizzard to the anus. This is the earthworm's main intestine and all of the food digestion and absorption takes place here.
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9
Find the lightly colored tissue that is near the earthworm's hearts. These are called seminal vessels and serve as the earthworm's reproductive organs. You will also notice small, white organs that are near the heart as well. These are more reproductive organs.
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10
Push the intestine to the side with your forceps. Underneath the intestine you will see what looks like a long, white string that runs along the entire length of the earthworm. This is called the ventral nerve cord.
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11
Cut the rest of the worm open after you've finished observing the above organs. Once the worm is open all the way, you will notice that the earthworm's ventral nerve cord and intestine truly go from the very top to the very bottom of the earthworm.
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