Excretion in the Blood-sucking Bug, Rhodnius Prolixus Stal. 3. the Control of the Release of the Diuretic Hormone.

It seemed reasonable to suppose that the release of the hormone was stimulated nervously or Immorally or both. The possibility of nervous control was examined first. Various of the nervous connexions to the ganglionic mass (Fig. 1) were cut, the insects were fed and the amount of urine subsequently produced was measured as described elsewhere (Maddrell, 1964). After diuresis the insects were dissected and the success of the operation was checked. The results of these experiments are displayed in Table 1. Clearly, no nervous information from the head or thorax is involved in the diuretic response. Cutting the nerves to the abdomen, however, abolished the response. Nunez (1963) attributed the absence of diuresis in such insects to the sectioning of the axons of the neurosecretory cells responsible for the release of the diuretic hormone. Two lines of evidence support a different explanation. Recent experiments with ligated fed insects (Maddrell, 19636) have shown that diuretic hormone can only be found in haemolymph samples collected from parts of the insect that include the fused ganglionic mass in the mesothorax. Neurosecretory cells with axons release their products at the ends of the axons (Herlant-Meewis & van Damme, 1962); if cutting the abdominal nerves in Rhodnius does interrupt the neurosecretory pathway involved in the release of the diuretic hormone, then the cell bodies of the neurosecretory cells must lie in the abdomen and the axons run into the gangli-