How does Small tube connect the dorsal and ventral vess

How does Small tube connect the dorsal and ventral vessels throughout the animal except in the segments 7 and 11 for the
http://www.transtutors.com/university-brock/anatomy-earthworm-6.htmearthworm anatomy and its
http://www.transtutors.com/university-brock/digestive-system-earthworm-6.htmdigestive system of earthworm which can be related together to get the
http://www.transtutors.com/biology-homework-help/earthworm/circulatory-systemcirculatory system of earthworm where they keep the blood flowing. Not true hearts they are called
http://www.transtutors.com/university-brock/reproduction-process-earthworm-6.htmaortic arches?
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