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The other corresponds to the subintestinal vein and the ventral vessel of the worms. With the formation of these organs the progressive development of the Ascidia comes to an end, and degeneration sets in.
Inside we find the first blood-vessels, an upper or dorsal vessel, corresponding to the aorta, between the gut and the dorsal cord, and a lower or ventral vessel, corresponding to the subintestinal vein, at the lower border of the gut. Now, the gills or respiratory organs also are formed at the fore-end of the alimentary canal.
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