The formation of the definitive excretory system (nephridium and bladder complex) in Hirudo medicinalis during the last two thirds of embryonic development was observed with light- and electron microscopy, immunocytochemistry, and nuclear labeling. In jawed leeches, two excretory systems develop and function successively. The nephridia of the cryptolarva are associated with the larval sac and persist until the definitive nephridia are sufficiently developed to be functional. Development of the definitive excretory system begins with the differentiation of the (ectodermal) bladder and urethra. The cells from which they arise incorporate bacteria and are thereby recognizable at day 8. The (mesodermal) urine-forming tissues of the nephridium (canalicular cells and central canal cells) appear a day later. By day 17, the nephridia are in contact with the outlet region and structurally able to function. Each nephridium is individually innervated by a peripheral neuron, the nephridial nerve cell, which expresses FMR Famide-like immunoreactivity and begins growing into the nephridium on day 11. Organogenesis of the leech nephridium is compared with the formation of excretory organs in other species. The temporal correlation of innervation and the development of the transporting cells is discussed.

Organic anion concentrations in the blood of Hirudo medicinalis were determined in samples from individual animals using reverse-phase high-pressure liquid chromatography (HPLC) and ultraviolet detection. Quantitatively important anions were malate, α-ketoglutarate, succinate, lactate and fumarate, constituting about 70% of total blood anions. Malate had the highest concentration, 34–68 mequiv I−1 blood, which could (depending on metabolic state) exceed the level of blood Cl− (approx. 36 mequiv I−1). Organic acid concentrations in the blood were considerably higher than in the tissue. Blood organic acid concentrations changed more with POO2 than with temperature. They were unaffected by short periods of aerobic exercise, but stress due to handling and prolonged restraint led to a drastic increase of blood lactate and succinate levels, while malate, fumarate and a-ketoglutarate levels decreased. After feeding on hypertonic, Cl−-rich meals, the Cl− concentration in leech blood increased far more than the cation concentrations. This was not compensated by a decrease of organic acid levels. The regulatory mechanisms for inorganic and organic ion homeostasis function independently.

Fluid secretion by isolated upper and lower portions of Malpighian tubules in the centipede Lithobius forficatus L. was studied. Ion requirements, cellular and transepithelial potentials, dependence on external osmolality and the effects of an insect diuretic factor and transport-active drugs were investigated. Unlike many insects, L. forficatus exhibited strongly Na+-dependent, K+-independent urine formation. However, as in many insects, upper and lower tubule portions from L. forficatus produced a K+-enriched, hypertonic fluid, and the transepithelial potential was positive with respect to the haemolymph. Furthermore, furosemide (5×10−4moll−1) reversibly inhibited urine formation. Ouabain, even at 10−3moll−1, had little effect on urine flow rate in upper tubules but inhibited secretion in lower tubules, albeit not completely. Locust diuretic hormone (at 10−7moll−1) enhanced fluid secretion in L. forficatus, but its action was not mimicked by dibutyryl cyclic AMP. The results suggest that some characteristics attributed exclusively to insects are common to non-insect arthropods.