The setae are solitary, 8, sometimes many, arranged in a ring shape, with 1-2 pairs of testis, usually at10-1node, and a pair of male reproductive pores, which are located on two or more somites behind the posterior testis, namely/kloc-0. A pair of ovaries, located at 13, have thick bands and few yolk.
Extended data:
The structure of earthworm's vascular system is complex, for example, there is a dorsal blood vessel on the back of earthworm's digestive tract. Because the muscles on the blood vessel wall are well developed, there is still a valve in the tube, and the blood is forced to flow from back to front by its wave-like contraction.
The blood vessels in the back and the heart determine the direction of blood flow. After the blood in the dorsal blood vessels flows to the front of the body surface, part of the blood is distributed to the esophagus, pharynx and brain, and most of the blood flows into the abdominal blood vessels through four pairs of hearts.
There are also valves in the heart that can beat rhythmically and control the flow of blood. Abdominal blood vessels are located on the ventral surface of digestive tract and cannot beat. Blood in the abdominal blood vessels flows from front to back. Abdominal blood vessels have vascular branches at each segment, which are distributed to the body wall, intestine and renal duct, where a microvascular network is formed.
After the exchange of gas and substance, the blood in the anterior 14 segment flows into the esophageal blood vessels on both sides of the digestive tract, and the exchanged blood flows into the neurovascular under the abdominal nerve after the 14 segment. Esophageal blood vessels are connected with nerve blood vessels, and blood flows from front to back.
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