MICTURITION IN THE CRAYFISH AND FURTHER OBSERVATIONS ON THE ANATOMY OF THE NEPHRON OF THIS ANIMAL

¹ From the Department of Zoölogy, The Johns Hopkins University, and the Department of Tropical Medicine, The Tulane University

1. The internal anatomical features surrounding the urinary outlet of the crayfish are described in detail for the first time.

2. Urine is retained in the bladders evidently by the ureteral syncytium, which is here described for the first time. There is no other way, conceivable to the writer, by which urine can be retained. Fibers do not insert on the operculum of the nephropore.

3. Urine is discharged by a localized rise in the haemocoelic pressure and can be expelled by direct action of the crop-gizzard on the bladders. Adequate electrical stimulation cannot cause contraction of the bladder but often evokes generalized motor activity.

4. Occasional abrupt spurts of urine, which were almost simultaneous from both nephropores, extended to the distance of a foot or more.

5. Destruction of the opercula before urinary collection has no rationale.

6. The bladder is innervated by fibers from the tritocerebral lobe of the brain. These fibers are doubtless mainly if not entirely afferent. The kidney is not innervated.

7. There is no valve between the nephric tubule and the bladder.

8. There is no valve or sphincter between the coelomosac and the labyrinth.

9. The epithelium of the coelomosac, the most proximal portion of the nephron, has been studied in detail. "Holocrine" secretion evidently does not occur because no mitotic figures could be found. The histological, chemical, and phylogenetical data contra-indicate filtration through the coelomosac.