Earthworm Dissection

Students will use the following tools for the earthworm dissection

• Scalpel

• Probes

• Dissecting Pins

• Rubber Padded Dissecting Tray

Scalpel

Probe

Dissecting Pins

Dissecting Pan

Before you start dissecting, find the following:

• Mouth

• Setae – the bristles used for locomotion. They are located by rubbing your fingers along the earthworm’s body. They are often times easier to feel than to see.

• Sperm Duct

• Clittelum

Sperm Duct

Sperm Groove

sperm moves along here from sperm duct to another worm

Oviduct

tube through which eggs pass

Clittelum makes mucus

Setae – bristle like structures that help the worm move

Mouth

Pin your worm at the tip of the mouth and at its midpoint.

Start your incision 2 cm behind the clittelum.

Make sure not to cut too deeply.

Continue your cut to the mouth

Begin to separate the skin using pins

Pin the skin back as you go along the cut. Angle your pins outward so that are out of the way.

As you pin the skin back, take your probe and break the partitions between the segments. These are called Septum.

A comparison of systems…

Circulatory System

“veins” carries blood to the “heart”

“arteries” carries blood away from the “heart”

“heart”

• Aortic Arches - surround the esophagus and function in pumping the blood throughout the body

Aortic Arches – Earthworms have 5 pair of these simple hearts.

Aortic Arch

• Ventral Blood Vessel- carries blood from the aortic arches to the rest of the body

• Dorsal Blood Vessel- Returns blood to the aortic arches and has valves to prevent backflow

Digestive System

• Food goes from the:

Mouth Pharynx Esophagus Crop Gizzard Intestine Anus

• Mouth- opening at the end allowing the intake of food consisting of particles of both living and dead substances

Mouth

• Pharynx- moves food from the mouth to the esophagus

Pharynx

• Esophagus- Carries food between the pharynx and the crop

• Crop – Stores food

Crop

• Gizzard – grinds food

Gizzard

• Intestine – Digests food

Dorsal Blood Vessel

Intestine

• Anus – where excrement (poop) comes out

Nervous System

• Ganglion- group of nerves. In the earthworm, there is a pair of ganglia in each segment and a cerebral ganglia acts like a brain

Brain

Nerve Cord and Brain

• Ventral Nerve Cord- connects the ganglia in each segment of its body with the cerebral ganglia. It coordinates movement

Ventral Nerve Cord

Ventral Nerve Cord

Reproductive System

• Earthworms are hermaphrodites which means they have both male and female body parts

Seminal Vesicles- store sperm produced by the earthworm

Seminal Receptacles

paired organs that store sperm received from another worm during copulation