Earthworm Dissection
Formal Lab write up Due Date – POSTED ONLINE
Points: 175 Lab points
Objective: Dissections are a key way to learn the anatomy of various
organisms. We will be learning about the anatomy of the earthworm
(Lumbricus terrestris. This specimen is a great introduction to the general
anatomy of invertebrates.
WARNING: If specimens are treated in any way inhumanely you will
receive a 0 on this lab. If you mess around or abuse the equipment you will
receive a 0 on this lab. This will DROP your semester grade by 5 to 10
percentage.
Procedures:
1) Gather the following materials: 15 pins
Scalpel
Dissection tray
Earthworm
Forceps
Probe
Scissors
2) Begin by identifying the features pointed out in figure 1. You will
need to draw the external anatomy of the Earthworm and label the
parts in the observation section of you lab. Each term you label you
will want to give me the function.
3) Lay the earthworm on the dissecting tray so the dorsal side of the
animal is up. The dorsal side feels smooth and is typically darker in
color than the ventral side. Place two pins through the sides of the
third segment back from the mouth and one through the caudal end.
4) With your scalpel make an incision from the clitellum down the
middle to the mouth. YOU DO NOT WANT TO CUT DEEPER
THAN 1/16th of an inch into the worm. You just want to be able to
reach the coelom. IF YOU CUT TOO DEEP YOU WILL RUIN
YOUR SPECIMEN!!
5) Now make a cut down each side of the clitellum toward the ventral
side. Grasp the skin with the forceps and carefully separate the septae
away from the body wall. Work your way toward the mouth pinning
the muscular body wall down and away from the internal organs.
Draw what you see in your observation section.
6) Now cut the sides (the skin) off the worm so all that is left is the
organs and the underside of the worm. Now cut straight through the
clitellum so all that remains is the head.
7)You should now be able to see most of the respiratory and circulatory
system. I want you to draw just the circulatory and respiratory systems
without including the digestion or the nervous system. Look at Figure
17-16 in your Zoology (POLAR BEAR) or Figure 17-12 (PANDA
BEAR) book as a reference.
8)You will now observe the digestive system of the worm. I want you to
draw, label and define all parts from the mouth to the anus.
9) With your worm flip it so the ventral side is exposed. Cut from the
clitellum towards the anus. Make sure this is also a shallow incision.
This will expose the ventral nerve cord, a long thread-like structure with
extensions going away dorsally. Draw what you see in the observation
section of your lab.
10)Separate one metamere from the caudal end of a worm so you have a
cross cut. Draw the cross section and define the terms listed in the lab
figure 3.
11) In the conclusion section of your lab, I want to summarize how the
digestive, circulatory, respiratory and nervous systems work.
12) All equipment must be washed and presented to the teacher.
Earthworms must be disposed of properly.