Earthworm Dissection
­ review organization
­ review gut systems
­ dissection
­ appropriateness
­ care/safety
­ equipment
­ start guide
­ label/colour
­ cleanup
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Cells, Tissues, Organs and Organ Systems
Organisms are made up of cells that are organized into groups, and groups of groups.
cells­­> tissues­­>organs­­>organ systems­­>individual
secretory­>stomach lining­>stomach­>digestive system
­>Cole
2 way, 1 opening
1 way, 2 opening
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Earthworm Dissection
Part A: Observing External Anatomy
1. Find the anterior (front) end of the earthworm. At the anterior end you will find the mouth.
2. Find the posterior (back) end of the earthworm. At the posterior end, there is an opening called the anus
to eliminate waste.
3. About one third of the way back from the mouth, you should see a thicker, smoother section of the worm
that is sort of saddle shaped. This is called the clitellum and is important in reproduction.
4. Earthworms belong to the phylum of segmented worms called Annelida. Each segment is separated by a thin wall called a septum.
5. The dorsal (back) surface of the earthworm is rounded and the ventral (belly) surface is flattened. Lightly
rub your finger along the ventral side toward the posterior end of the worm. You should feel tiny bristles
called setae that anchor the earthworm as it moves through the soil. Try to find the setae with a magnifying
glass.
6. With your magnifying glass, look for tiny pores on each segment. Liquid wastes are eliminated through these
pores. Near the front end of the worm, you should see some larger pores that can be seen easily without
magnification. These are genital pores that are important in reproduction.
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Part B: Dissection to Observe Internal Anatomy
1. Lay the worm on your dissecting tray with the dorsal side up. Secure each end of the worm to the tray with dissecting pins.
2. Start your dissection about 4 cm posterior to the clitellum. Lift up the skin with a pair of forceps
and snip an opening with a pair of dissecting scissors. Make sure that you don't go too deep! Cut
in a straight line all the way through to the mouth. Go slowly and be sure to cut just the skin!
3. Use a blunt probe to drag along the inside of the skin to break the septum walls and spread the skin.
Pull apart the two flaps of skin with forceps and pin them flat on the tray.
4. Use the diagram you have been given to locate all of the parts of the earthworm.
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5. Label the following parts on your diagram:
Diagram A:
mouth
seminal receptacle openings
male/female openings
clitellum
setae
Diagram B:
brain
pharynx
esophagus
pseudo hearts
seminal vesicle
dorsal blood vessel
crop
gizzard
intestine
mouth
ventral blood vessel
ventral nerve cord
6. Colour the digestive system green, the gas­exchange surface blue, the nervous system yellow
the reproductive system purple and the circulatory system red (where possible).
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