They are said to be developed from the coelomic epithelium which covers the efferent vessel or its caeca.
The male ducts are either one pair or two pairs, which open by a common and complicated efferent terminal apparatus furnished with a protrusible penis.
Each auricle forms the terminal enlargement of the efferent vein of the ctenidium of its own side.
By the pulsation of the pericardial vesicle (best observed in the larva) the blood is driven into the glomerulus, from which it issues by efferent vessels which effect a junction with the ventral (sub-intestinal) vessel in the trunk.
G, The branchial efferent vessel.
The gonads, as in other Arthropoda, are hollow saccular organs, the cavity communicating with the efferent ducts.
One of these branches communicates with the afferent lophophoral vessel, while the other one opens into the crescentic efferent lophophoral vessel (r.v.).
These processes are hollow, and receive the venous blood from, and return it again aerated into, the hollow axis, in which an afferent and an efferent blood-vessel may be differentiated.
A, Of Chiton: f.t., fibrous tissue; a.b.v., afferent blood-vessel; e.b.v., efferent blood-vessel; g.l., laterally paired lamellae.
Each testis communicates by means of an efferent duct with a common collecting duct of its side of the body, which opens on to the exterior by means of a protrusible penis, and to which is sometimes appended a seminal vesicle.