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Earthworm Dissection
Introduction: The main objective of any dissection is to expose organs to help one understand the form and function of an
organism. Be careful not to destroy them because they are wonderful to see exposed to view.
Materials: Night crawlers (earthworms), razor, scissors, forceps, straight pins, probe/dissecting needle/toothpicks, paper towel
Procedure: Day . A look at the worm and how it moves.
1.
Measure the length of the worm in cm. _________. Count the number of segments on your specimen. ______________.
2.
Hold the worm and rub your fingers along its lateral surfaces. What do you feel? ________________________________
What are these structures called? ____________. What is their function? __________________________________________
Diagram 1. External features of the earthworm. Label this diagram.
Title of drawing:…………………………………………………………………………………………………………
Diagram 2. Locomotion in an earthworm: Three successive stages of contraction and relaxation of segments.
Stage 1
Stage 2
Stage 3
Day 2. Cutting the worm open.
1.
Place the preserved worm ventral side down on the dissecting tray. Make sure the dorsal (back) side is facing up at you.
The dorsal surface should be darker in color than the ventral side.
2.
Gently stretch and pin the worm to the tray at the anterior and posterior ends. Measure about 2 cm. behind the clitellum;
make a small horizontal cut with the razor in the body wall. This will allow you to place the scissor's point into the body
cavity (coelom) . Now cut upward and forward ( anterior), until you reach the very end of the worm.
3.
You will notice that the body wall of the worm will not move down into a flattened position. It is being held in position
by small internal walls called septa. These septa must be cut in order for the body wall to lay flat. Use your probe to
break these septa.
4.
Now pin down the body wall. Make sure you use as few pins as possible. This will allow you to see the internal organs
clearly.
5.
Locate the tube like digestive system. Identify the following parts and label them on figure.1 Mouth, pharynx,
esophagus, crop, gizzard, and intestine. Use the space below, and start the diagram of your own dissection now.
6.
Examine the dorsal surface of the digestive system. Notice a black line running down its entire length. This is the dorsal
blood vessel. Label it on fig.1.
7.
The earthworm contains _________ aortic arches. Locate them surrounding the esophagus. Label them on fig.1.
8.
With your probe, push aside the intestine and locate the ventral blood vessel and nerve cord. label them on fig.1.
9.
Identify the earthworm's reproductive structures, located along side the esophagus. The first set of lightly colored organs
are the seminal receptacles. What is their function? _________________________
Posterior to them are the larger seminal vesicles. They function in______________________________________. Label these
reproductive organs on fig.1.
10.
The earthworm removes its nitrogenous waste through small tube-like structures called nephridia. Each segment contains
2 nepherida, one on each side of the alimentary canal. Locate the nephridia on figure 1 and label them.
Figure 1
Figure 2.
A labeled drawing of your dissection
Summary and discussion questions:
1.
How many segments does your specimen contain? ____________. How did you arrive at the above answer? ____
_____________________________________________________________________________________________.
2.
How many setae does it contain? _________________
How did you arrive at the answer? ____________________
______________________________________________________________________________________________.
3.
Describe the texture of the crop and gizzard. ___________________________________________________________
__________________________________________________________________________________________________
4.
Why are of the crop and gizzard so different in texture?___________________________________________
_____________________________________________________________________________________________
5.
How do the form and shape of the earthworm relate to how they live? ______________________________________
___________________________________________________________________________________
6.
What is a hermaphrodite? ____________________________________________________________
__________________________________________________________________________________
7.
What organs does the earthworm use to remove nitrogenous waste from its body? ___________________________
_________________________________________How many are there?_________________________________________
8.
Explain how the earthworm's circulatory system is similar and yet different to ours?
Similarities__________________________________________________________________________________
Differences__________________________________________________________________________________
Describe the earthworm’s digestive system._________________________________________________________
__________________________________________________________________________________________________
__________________________________________________________________________________________________
________________________________________________________________________________________________
9.
Compare the earthworm’s digestive system to ours.
Similarities_________________________________________________________________________________________
__________________________________________________________________________________________________
__________________________________________________________________________________________________
Differences_________________________________________________________________________________________
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