How to Disect an Earthworm
People often become interested in earthworms and they want to learn more about them. Earthworms make the soil rich when they build tunnels, which helps plant life grow. Earthworms are important to the ecosystem because they have the ability to decompose dead plant and animal material. Dissecting the earthworm will teach you about the physical structures and segments. Once you dissect earthworms, you can observe them internally and externally more closely.
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Things You'll Need
- Earthworm diagram
- Preserved earthworms (5 to 8 inches)
- Rubber gloves
- Dissection tray
- Scalpel
- Forceps
- Dissection pins
- Trashcan
- Rubbing alcohol or diluted bleach
Instructions
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1
Look at a diagram of an earthworm. Study the internal and external parts of the earthworm before you begin to familiarize yourself with the anatomy of the earthworm you will dissect.
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Lay the earthworm vertically on a dissection tray with the dorsal (back) side facing up. Wear rubber gloves to protect your hands.The dorsal side of the earthworm appears darker in color because the dorsal blood vessel runs on the top of the digestive track under the skin. Observe the exterior of the earthworm before you begin looking at its interior.
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3
Examine the anterior (front) and the posterior (back) of the earthworm. The anterior will be thicker than the posterior. Locate the clitellum, or the swelling close to the earthworm's head.
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Examine the body of the earthworm. Count its segments. The segments of an earthworm are visible externally. They appear as rings, and they separate the internal partitions of the worm. Look closely to see the pores and small setae, or hairs. Setae are located on each segment, except the first and last segments, and they appear as small bristle or hair-like structures. The setae help the earthworms move and feel the environment. The pores are where the genitalia are located for the worms to reproduce.
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Turn the earthworm over to look at the bottom or dorsal side. Use a scalpel to make a shallow cut from the anterior of the worm to the middle of its body. Avoid making the cut too deep.
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Open the skin of the earthworm gently with forceps. Pin the skin down to the dissection pan. Repeat this process for the second half of the earthworm's body. Cut from the posterior of the earthworm's body to the middle, and pin it to the dissection tray.
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Use the diagram to locate the organs of the earthworm. Look for the gizzard, crop, esophagus and ventral nerve cord. The gizzard is a sack behind the mouth that squeezes and contracts so that the earthworm can chew its food. The crop is a large organ located in the digestive tract used to help break down food into smaller pieces. The esophagus is also part of the digestive tract and it sits between the pharynx and the crop. It helps to move the food from the pharynx to the crop. The ventral nerve cord connects the ganglia in each of the segments of the body with the brain. The ganglia help to coordinate the movement of the worm.
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8
Dispose of the earthworm and earthworm parts in a trash can designated solely for the earthworms. The earthworm parts can be placed outdoors for the wildlife if no chemicals were used during dissection. Clean the instruments with rubbing alcohol or diluted bleach to sanitize them.
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Tips & Warnings
Minors need to be supervised when using sharp instrument. Always have someone monitor the dissection.
References
- Photo Credit earthworm image by ril from Fotolia.com
