Archive image from page 185 of The cyclopædia of anatomy and. The cyclopædia of anatomy and physiology cyclopdiaofana01todd Year: 1836 170 ANNELIDA. sides (d), which are highly contractile. These ' moniliform vessels' are placed in a situation corresponding to the ovaries : they are directed downwards and open into a ventral vessel (6), which occupies the middle line of the inferior aspect of the animal, following the same track as the sub-nerval vessel, but situated less superficially. Its parietes are contractile, and it may be seen alternately dilating and con- tracting simultaneously at
Archive image from page 185 of The cyclopædia of anatomy and. The cyclopædia of anatomy and physiology cyclopdiaofana01todd Year: 1836 170 ANNELIDA. sides (d), which are highly contractile. These ' moniliform vessels' are placed in a situation corresponding to the ovaries : they are directed downwards and open into a ventral vessel (6), which occupies the middle line of the inferior aspect of the animal, following the same track as the sub-nerval vessel, but situated less superficially. Its parietes are contractile, and it may be seen alternately dilating and con- tracting simultaneously at every part along the whole of its extent. The blood flows into this ventral vessel from before backwards, and leaves it to re-enter the dorsal vessel by passing through the branches (e) which ascend perpendicularly to join the latter, on either side of the alimentary canal, which they thus embrace, and to which they furnish a great number of ramifications. The blood con- tained in the sub-nerval vessel flows equally from before backwards, and ascends to re-enter the dorsal vessel by lateral channels (_/'), ana- logous to the anastomosingvesselswhich we have just described, but situated more superficially than those. These superficial transverse or dorso-ubdominal vessels, as they are termed by M. Duges, severally receive a large branch from their corresponding deep-seated dorso- abdominal vessel, and distribute to the skin a number of ramifications which appear to be specially destined to bring the blood into contact with the oxygen necessary for respi- ration. In the genus na'is the moniliform vessels, which in the earthworm perform in some degree the office of a composite heart, seem to be re- placed by a single pair of wide veins, which are contractile and analogous to a divided heart, and both the superficial and deep-seated transverse vessels by which the blood ascends to the dorsal trunk seem to rise from one and the same ventral trunk; so that the circulatory appa- rat
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