The Circulatory System Earthworms have a closed circulatory

The Circulatory System • Earthworms have a closed circulatory system which is an evolutionary advantage over animals with an open system (like the grasshoppers) • The blood travels towards the posterior through the ventral blood vessel & then back towards the anterior end through the dorsal blood vessel

• The ventral & dorsal blood vessels are connected by five pairs of muscular tubes called aortic arches • The aortic arches pump the blood from the dorsal blood vessel to the ventral blood vessel to continue the process • Just like humans, the blood carries oxygen, carbon dioxide, nutrients & wastes

The Respiratory System • Worms have moist skin that allows for gasses to diffuse through it - oxygen in & carbon dioxide out • There is a network of tiny capillaries just under the skins surface that collect & release these gasses • The skin also secretes mucus to protect it from drying out

The Excretory System (urine production) • Each segment of the earthworm, other than the first three and the last one contains a pair of nephridia • Nephridia are small tubules that release cellular wastes out of small pores on the ventral surface of the worm

The Nervous System • The nervous system consists of a chain of ganglia connected by a ventral nerve cord • Most segments contain a single ganglion • Nerves branching from each ganglion carry signals to the muscles & from the sensory cells in that segment

• The sensory information is sent to the main ganglion in the head portion called the cerebral ganglion

The Reproductive System • All earthworms are hermaphrodites however, they cannot fertilize their own eggs • Each worm has a thickened section of their body, towards the anterior end called the clitellum • The clitellum secretes a thick mucus into which the earthworm releases sperm

• When another earthworm moves next to another’s clitellum, the sperm is deposited into its seminal receptacles • The sperm is stored until the eggs are ready for release • When the eggs are fertilized, the clitellum secretes a thick, tough mucus packet that the eggs are placed into before being dropped to the ground

The End