Biology Lab || Earthworm Dissection

Anatomy of an Earthworm: External and Internal Structures

Introduction to Earthworms

• The earthworm is a segmented worm with complex anatomy, commonly seen in soil. This lab focuses on examining both its external and internal structures through dissection.

Identifying Key Anatomical Features

• The anterior end of the earthworm, closest to the clitellum (a reproductive structure), contains the mouth, while the posterior end has the anus.

• Distinction between dorsal (darker side) and ventral sides is crucial for making incisions during dissection. Most internal organs are located in the anterior region.

Dissection Procedure

• Pins are used to secure the worm in place before making incisions; a transverse incision is made on the dorsal surface behind the clitellum.

• Careful cutting through epidermis and cuticle is necessary to avoid damaging internal organs. The coelom, a hollow body tube containing organs, is revealed after cutting septa.

Observing Internal Organs

• The digestive system includes parts like pharynx, esophagus (not visible), crop, gizzard, and intestine. Solid waste exits through the anus as castings that enrich soil.

• Earthworms possess a simple nervous system with ganglia functioning similarly to a brain. The ventral nerve cord runs along its length.

Reproductive and Circulatory Systems

• Earthworms are hermaphrodites producing both male and female gametes; testicles produce sperm while seminal receptacles store it from other worms.

• Lacking a respiratory system, earthworms exchange gases through their skin. They have a circulatory system with five pairs of muscle-lined blood vessels called aortic arches.

Conclusion on Earthworm's Role