Name: __________________________________
Lab # ________
Lab #
Date: ___________
: Earthworm Dissection
Virtual Lab: http://www.mhhe.com/biosci/genbio/virtual_labs/BL_14/BL_14.html
Procedure:
Part I – Terminology
1. There are several terms you should be aware of before beginning your dissection. These words will help you orient
yourself when you dissect your worm.
▪
Anterior - ________________________________________________________________________
▪
Posterior - ________________________________________________________________________
▪
Dorsal - __________________________________________________________________________
▪
Ventral - _________________________________________________________________________
▪
Clitellum - ________________________________________________________________________
Part II. External Anatomy
1. Examine your earthworm and determine the dorsal and ventral sides. Locate the
two openings on the ventral surface of the earthworm
2. The openings toward the anterior of the worm are the sperm ducts.
The openings near the clitellum are the genital setae.
3. Locate the dark line that runs down the dorsal side of the worm, this is the dorsal
blood vessel. The ventral blood vessel can be seen on the underside of the worm,
though it is usually not as dark.
4. Locate the worm's mouth and anus.
5. Note the swelling of the earthworm near its anterior side - this is the clitellum.
6. Label the diagram to the right using the bold words above AND draw in the
blood vessel.
7. Each segment of a worm has small pairs of bristles called setae which help it
move. Run your fingers up and down the ventral side of the worm to fell the
bristles.
Part III. Internal Anatomy
1. Place the specimen in the dissecting pan DORSAL (top) side up. Push one pin through the anterior end of the
worm (near the mouth) and one through the posterior.
2. Locate the clitellum and insert the tip of the scalpel/scissors about 3 cm posterior (towards the anus)
3. Cut carefully all the way up to the head. Try to keep the scissors pointed up, and only cut through the skin.
4. Spread the skin of the worm out, use a teasing needle to gently tear the septa (little thread like structures that
hold the skin to organs below it)
5. Place pins in the skin to hold it apart. It should look like the diagram below:
OBSERVATIONS:
Reproductive System
1. Earthworms have both male and female reproductive organs, but does not fertilize itself. Earthworms
reproduce sexually by lining up and exchanging sperm. The clitellum secretes mucus that picks up the egg and
sperm cell forming a cocoon. The cocoon is dropped into the soil where a new earthworm develops. NOTE: The
ovaries and testes are there but too small to see. An earthworm’s reproductive system has the following parts.
Locate these parts & write the function:

Clitellum: ______________________________________________________________________________

Seminal Vesicles: _______________________________________________________________________

Seminal Receptacles: ____________________________________________________________________
2. The first structures you probably see are the seminal vesicles. They are located toward the anterior of the
worm. These are used for producing sperm. What color are they in the earthworm?
____________________________
3. Use tweezers to remove these structures from the worm. They lie on top of the digestive system.
Circulatory system
1. Earthworm’s have a closed circulatory system which means all body fluids are contained within small tubes. An
earthworm’s circulatory system has the following parts. Locate these parts on the write their function:

Aortic Arches (Hearts): ____________________________________________________________________

Dorsal Blood Vessel: ______________________________________________________________________
2. The dorsal blood vessel appears as a dark brownish-red vessel running along the intestine. The heart (or aortic
arches) can be found over the esophagus (just posterior to the pharynx). Carefully tease away the tissues to
expose the arches of the heart, they run across the worm. If you are careful enough, you can expose all 5 of
them
3. The ventral blood vessel is opposite the dorsal blood vessel, and cannot be seen at this time because the
digestive system covers it.
Label the diagram below (use the bold words from above):
Digestive System
1. The digestive system starts at the mouth. You will trace the organs all the way to the anus and identify each on
the worm.
2. Find the mouth opening, the first part after the mouth is the pharynx, you will see stringy things attached to
either side of the pharynx (pharyngeal muscles). The esophagus leads from the pharynx but you probably
won’t be able to see it, since it lies underneath the heart. You will find two structures close to the clitellum.
First in the order is the crop, followed by the gizzard. The gizzard leads to the intestine which is as long as the
worm and ends at the anus.
After you have located the parts of the earthworm’s digestive system, describe their functions:

Mouth: __________________________________________________________________________________

Pharynx: __________________________________________________________________________________

Esophagus: ________________________________________________________________________________

Crop: ____________________________________________________________________________________

Gizzard: __________________________________________________________________________________

Intestine: __________________________________________________________________________________
Nervous System
1. Earthworms have a simple nervous system which allows the worm to sense its surrounding. The brain is very
small and usually hard to see. A nerve cord is located on the ventral side. Locate the nerve cord & write the
function.
▪
Ventral Nerve Cord: __________________________________________________________________
Label the following diagram of the earthworm using the word bank:
2. ____
3. ____
8. ____
4. ____
1. ____
5. ____
6. ____
7. ____
15. ___
10. ____
14. ____
13.____
12.____
11. ____
a. Mouth
h. Dorsal Blood Vessel
b. Pharynx
i. Ventral Blood Vessel
c. Esophagus
j. Clitellum
d. Crop
k. Seminal Vesicles
e. Gizzard
l. Seminal Receptacles
f. Intestine
m. Ventral Nerve Cord
g. Aortic Arches (Hearts)
n. Brain
h. Dorsal Blood Vessel
i. Ventral Blood Vessel
j. Clitellum
k. Seminal Vesicles
l. Seminal Receptacles
m. Ventral Nerve Cord
n. Brain
9. ____