Hearts of earthworm are essentially large, while the cockroach heart has 13 chambers.

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"The hearts as well as some of the blood vessels of earthworm are all in front region of body before the dark brown band called clitellum. Their hearts are essentially, large, muscular tubes, pulsatile and contractile. The earthworms for the first time in animal kingdom, developed pumping hearts.

A cockroach has a chain of hearts, in all totaling to 13. Some regard it as a single heart with 13 chambers. These are funnel shaped chambers with a pair of tiny holes called ostia. The ostia allow blood into the cockroach hearts. The hearts push the blood forward, in the direction of the head. Beneath the hearts are rhomboid alary (i.e. wing-shaped) muscles. Contraction and relaxation of the alary muscles pulls the blood nearer heart and Suction pressure fills the heart with blood entering through the ostia."

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Source(s):
http://www.suite101.com/article.cfm/our_beautiful_bodies/104026

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