Though the paired arrangement of the nephridia is the prevalent one in the Chaetopoda, there are many examples, among the Oligochaeta, of species and genera in which there are several, even many, nephridia in each segment of the body, which may or may not be connected among themselves, but have in any case separate orifices on to the exterior.
The oviducts are always short trumpet-shaped tubes and are sometimes reduced (Enchytraeidae) to merely the external orifices.
On account of their position they were termed by him the " capito-pedal orifices," being placed near the junction of head and foot.
The gonapophyses are the projections near the extremity of the body that surround the sexual orifices, and vary extremely according to the kind of insect.
The great dorsal contractile vessel or " heart " of Limulus is closely similar to that of Scorpio; its ostia or incurrent orifices are FIG.