ABSTRACT
The anatomy, ultrastructure and innervation of the nephridia of the North American leech, Macrobdella decora (Say), are described. The osmotic concentrations of blood, crop fluid and final urine, as well as urine flow under normal conditions, were found to be similar to those of the well-studied European medicinal leech, Hirudo medicinalis L.
The capacity of the excretory system after changes in external salinity, and after salt and water loading with artificial blood meals, was investigated. In contrast to H. medicinalis, M. decora does not tolerate hypertonic environments and is less efficient in rapidly excreting excess salt and water. Three factors make salt and water regulation in M. decora different from that in H. medicinalis; a slower fluid resorption from the crop, a limited transport capacity of the primary urine-forming cells, and a lower rate of salt reabsorption in the central canal.
