In Lumbricus the connexion is a little closer; the funnel of the nephridium, in the segments in which the funnels of the gonad ducts are to be developed, persists and is continuous with the gonad duct funnels on their first appearance.
The sperm ducts are usually longer than the oviducts; but in Limicolae both series of tubes opening by the funnel into one segment and on to the exterior in the following segment.
The circular lip is extremely developed in Megalophrys montana, and its funnel-shaped expansion, beset on the inner side with radiating series of horny teeth, acts as a surface-float, when the tadpole rests in a vertical position; the moment the tadpole sinks in the water the funnel collapses, taking on the form of a pair of horns, curling backwards along the side of the head; but, as they touch the surface again, it re-expands into a regular parachute.
Vezhdovsky's figures of Rhynchelmis agree with those of Bergh in showing the backward growth of the nephridium from the funnel cell.
But the funnel is large and thus differs from the funnels of the nephridia in adjoining segments.
In both the cavity originally or immediately continuous with the coelom appears first in the funnel and grows backwards.
Rhynchelmis, which afterwards become by an enlargement and opening up of the funnel the permanent nephridia of the adult worm.
Bunsen may be regarded as the originator of the second method, and it was he who devised the small cone of platinum foil, sometimes replaced by a cone of parchment perforated with pinholes, arranged at the apex of the funnel to serve as a support for the paper, which is apt to burst under the pressure differences.
Oviducts of Oligochaeta, sperm ducts of Phreoryctes, the coelomoducts occupy, like the nephridia, two segments, the funnel opening into that in front of the segment which carries the external pore.
In Hirudo the funnel is not pervious and is composed of a large number of cells.