Whitman the entire nephridial system (in the leech Clepsine) is formed by the differentiation of a continuous epiblastic band on each side.
At the least there is no doubt that the genital funnels are developed precisely where the nephridial funnels formerly existed.
If the genital funnels are not wholly or partly formed out of the nephridial funnels they have replaced them.
Here also the genital funnels have either replaced or been formed out of nephridial funnels.
Here again the nephridial funnel seems to have been converted into or certainly replaced by a secondarily developed funnel.