Quarterly Journal of Microscopical Science, Vol s3-104, 217-225, Copyright © 1963 by Company of Biologists

The Dorsal Nerves of Cyclorrhaphan Larvae: Giant Cells in which Secretory Channels Appear at the Onset of Puparium Formation

¹ Department of Biological Sciences, Northwestern University, Evanston, Illinois, U.S.A.

Median dorsal nerves have been recorded in many Diptera Cyclorrhapha, but their histology has never been considered. It is shown here that they are very different histologically from the lateral segmental nerves. They are invested in a limiting membrane, have no nuclei other than a single large nucleus for each nerve, and the cytoplasm is homogeneous in appearance. These so-called ‘nerves’ are here considered to be giant cells. At the onset of puparium formation, granules appear in the cytoplasm, and this is followed by the establishment of interconnecting channels, disposed peripherally; changes are at the same time observable in the nuclei. The nerves are unbranched until the respective segment is reached; the distal ends of the nerves then give off fine nerve-terminals. The channels within the nerves are seen to converge and pass out into the terminals. These observations suggest that the ‘dorsal nerves’ are giant cells, their nuclei lying not within, but outside the central nervous system, showing considerable similarity to the secretory neurones and secretory nerves associated with the pericardial organs of Crustacea. The nerve-terminals pass to the segmental muscles and possibly play some part in tissue histolysis in the early pupa.

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