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Anatomy of an Earthworm

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Anatomy of an Earthworm - Lesson Summary

The cross-section of an earthworm shows that the body wall is covered by a thin layer of cuticle followed by a single layer of epidermis.  Below the epidermis lie two layers of muscles – circular and longitudinal muscles, followed by the innermost coelomic epithelium.

The longitudinal section of the earthworm shows a alimentary canal that runs from the first to the last segment of the body. The first segment bears the mouth, which opens into the buccal cavity, followed by a muscular pharynx, which continues into a narrow oesophagus which opens into the gizzard, which helps to grind soil particles and organic matter. Stomach has calciferous glands, whose secretion neutralises acid and  it continues into a long intestine, which has typhlosole for absorption. In the last segment anus is present.

Circulatory system consists of blood vessels, capillaries and hearts. Earthworms also have blood glands which produce blood cells and haemoglobin. These blood cells are phagocytic in nature. The hearts, which are important organs in the circulatory system, help circulate blood in one direction.
The nephridial system have several nephridia that function as excretory organs. There are three types of nephridia, namely septal, integumentary and pharyngeal. The septal nephridia are present on either side of the intersegmental septa. The integumentary nephridia are attached to the lining of the body wall. The pharyngeal nephridia occur as paired tufts on either side of the pharynx and oesophagus. All nephridia have similar structures and regulate the volume and composition of body fluids.

The nervous system consists of ganglia that are connected to a double ventral nerve cord. At the anterior end, the nerve cord bifurcates to form a nerve ring.  The cerebral ganglia along with other nerves in the ring integrate sensory and muscular responses of the body.  Earthworm have light, touch sensitive and chemoreceptor's which help them respond to any chemical stimuli.

Earthworm is hermaphrodite. The male reproductive system consists of two pairs of testes , vasa deferentia, the prostate gland and spermatic duct. Which opens to the exterior through a pair of male genital pores. Spermatheca, which receives and stores spermatozoa during copulation. The female reproductive system consists of a pair of ovaries, ovarian funnels, oviduct and a single female genital pore. During copulation, two worms exchange sperms. Later inside the cocoon fertilisation and development occurs, after three weeks, each cocoon produces about two to twenty baby worms. 

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