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How to dissect a worm

Earthworms are important helpers in the garden or field!

Their tunneling mixes up the soil and brings rich soil to the surface.

You can observe the organs of these tiny creatures by dissecting a preserved earthworm.

Our earthworm dissection guide will walk you through the entire process.

Earthworm Observation: External Anatomy

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1. Find the anterior (front) end of the earthworm by locating the fleshy bump over its mouth, called the prostomium. The posterior (back) end has a small hole where solid waste is expelled, called the anus. The length of the worm is made up of many tiny segments, each separated by a thin wall called a septum.

2. About one-third of the way back from the mouth you should see a thicker and smoother section of the worm. This is called the clitellum, and it is involved in reproduction.

3. Notice that the earthworm has a rounded dorsal (back) surface and a flatter ventral (belly) surface. Usually the dorsal surface is darker than the ventral surface (though sometimes this is obscured in the preservation process). Lightly rub your finger along the ventral side toward the posterior end of the worm. You should feel a roughness caused by tiny bristles called setae. Using a magnifying glass, try to see the setae.

4. With your magnifying glass look for tiny pores on each segment. Liquid wastes are expelled through these pores. Near the front end of the worm you should see some larger pores that can be easily seen without magnification. These are genital pores and are important in reproduction.

Earthworm Dissection: Internal Anatomy

1. Lay the worm on your dissecting tray with its dorsal side facing up. Use dissection pins to secure each end on the tray. Start your dissection about an inch posterior to the clitellum. Lift up the skin with a pair of forceps and snip an opening with a pair of dissecting scissors. Insert the scissors into the opening and cut in a straight line all the way up through the mouth. Go slowly and be sure to cut just the skin—if you go too deep you may damage the internal organs.

2. Using the forceps and dissection pins, carefully pull apart the two flaps of skin and pin them flat on the tray. (You may need to drag a pin along the inside of the skin to sever the septum walls to make it easier to spread the skin.)

How to dissect a worm
Click for full-size pdf

3. Look at the labeled picture to help you find the following features:

  • Pharynx: This is the light-colored organ just inside the mouth. Its muscular contractions pass food on down to the esophagus.
  • Hearts (or ‘aortic arches’): Behind the pharynx are five dark loops wrapped around the esophagus. These are the blood vessels that serve as the hearts of the worm.
  • Dorsal blood vessel: This is a dark line extending from the hearts over the top of the crop.
  • Crop: Food from the esophagus is temporarily stored in the crop.
  • Gizzard: Food comes from the crop into the gizzard, where it is ground up.
  • Intestine: The intestine is the long tube extending from the gizzard all the way to the anus. Food is digested and absorbed here.
  • Reproductive organs: The light colored tissue above and around the hearts are seminal vesicles. Other reproductive parts appear as small white organs on the ventral side of the hearts.
  • Ventral Nerve Cord: With your forceps, gently push aside the intestine to view the long white nerve cord running along the length of the worm beneath it.

4. Optional: Finish cutting the rest of the worm open from the first incision through to the anus. Observe how the intestine and ventral nerve cord both continue through the entire length of the worm.

See the rest of our online dissection guides for pictures of cow eye dissections, sheep brain dissections, and more.

What one customer said about the earthworm dissection guide:

“Good first dissection. The earthworms were in good condition, not smelly at all, and large enough to see the anatomy pretty well. My boys are 11 and 12, and neither wanted to dissect anything, but both found the dissection very interesting once they got started.”

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One of my favorite parts of Apologia Biology is the when we start dissections. Seriously. I love when the kids see first hand what we have been learning about in the text. I know that dissections can sound gross, but trust me, dissections make the curriculum come alive. Don’t skip them!

Dissections in Apologia Biology start with the earthworm. Earthworms are a great introductions to invertebrates and an easy dissection to start with. The organs and structures are so easy to see and examine. Even though the Apologia Biology is a high school course, I could see elementary students doing this lab with ease. My 10 year old had no problem with it.

How to dissect a worm

Don’t be scared away by the thought of dissections. They truly add to the science experience and understanding of science. If your students are interested in animals and their anatomy at all, you can do dissections even without a curriculum! There are great guides and lessons available.

How to dissect a worm

Earthworm Dissection Tips

If you have decided to do an earthworm dissection, I want it to be a great experience for you and your student. There is so much more to dissections than cutting up an animal.

Dissections allow us to examine the internal structures of organisms that we normally see only in textbook diagrams. Seeing the size, color, and shape of these structures up close adds so much to the understanding of how life works. Take some time to properly prepare to get the full benefits.

Get Good Dissection Tools

Good dissecting tools can make all the difference in your dissection experience. I’ve had people tell me how hard it was to do the dissections that their curriculum called for. Then, they tell me they were using a paring knife from the kitchen. Well, that’s the problem.

How to dissect a worm

Dissection tools aren’t that expensive and are easy to order. Make the investment. All you need is dissecting tools, dissecting pins, dissecting pans or foam plate, a specimen and a dissection guide. You can order them from may sources. I like Homeschool Science Tools and Nature’s Workshop Plus. Amazon, also, has some good dissection tool sets.

Order Quality Specimens

The quality of your specimens can make or break your dissection experience. Stick with tried and true resources like Homeschool Science Tools and Nature’s Workshop Plus for your specimens. You might find a cheaper price from other sources, but my experience has been old or damaged specimens. You get what you pay for.

Nothing ruins the experience like an earthworm that is so damaged that you can’t find the structures that you are looking for or one that is so old and smells so bad you can’t be in the same room with it!

How to dissect a worm

Get A Good Dissection Guide

The Apologia Biology curriculum has excellent dissection instructions. They take you step by step through the process and make it so easy. For an even greater experience and a personal dissection walk-through, get the Apologia Biology companion instructional DVD. It is fantastic!

If you are dissecting outside of a curriculum, look for guides from your specimen source.

Take Your Time

Give your students plenty of time for dissections. Don’t rush them. Sometimes they can be a bit squeamish about cutting into the specimen and that’s fine. Allow them some time to get accustomed to the idea, and then be ready to help them out. I have to admit that I don’t like the initial cutting into animals, but when the internal structures are revealed all unease disappears.

Earthworm Dissection Online Resources

There are lots of resources online that will help your earthworm dissection experience, too. Here are just a few I discovered.

How do you feel about dissections? Do you have any favorite dissection resources?