In Hirudo the funnel is not pervious and is composed of a large number of cells.
Low down on the leeward side it is dark red and fertile, but still too pervious to retain moisture well.
Nephridia always paired, rarely (Pontobdella) forming a network communicating from segment to segment; lumen of nephridia always intracellular, funnels pervious or impervious.
The conditions which favour the vitality, growth and multiplication of the typhoid bacillus are the following: the soil should be pervious; it should be permeated with a sufficiency of decaying - preferably animal - organic matters; it should possess a certain amount of moisture, and be subject to a certain temperature.
A perfect soil would be such a blend of sand, clay, chalk and humus as would contain sufficient clay and humus to prevent drought, enough sand to render it pervious to fresh air and prevent waterlogging, chalk enough to correct the tendency to acidity of the humus present, and would have within it various substances which would serve as food-materials to the crops.