Reference: Biol. Bull.. 160: 11-30. (February, 1981) HISTOLOGICAL AND PHYSIOLOGICAL ASPECTS OF THE MEDULLA EXTERNA X ORGAN, A NEUROSECRETORY CELL GROUP IN THE EYESTALK OF PALAEMON SERRATUS PENNANT (CRUSTACEA, DECAPODA, NATANTIA) CHANTAL BELLON-HUMBERT, FRANCOIS VAN HERP, 1 GODFRIED E. C. M. STROLENBERG, 1 AND J. MANUEL DENUCE 1 Laboratoire de Biochimie, Faculte de Medecine, Universite de Bretagne Occidental, 29279 Brest Cedex. France ABSTRACT The medulla externa X organ (MEX) is composed of two cell types containing two different categories of neurosecretory elementary granules also found in the sinus gland. Changes in the volume and activity of the organ were observed in relation to the intermolt cycle and season. After extirpation of the medulla externa X organ, the volumes of both the sinus gland and the organ of Bellonci increased in post-and intermolt stages. In the sinus gland, lysis and clumping were observed in axon endings containing one (large) granule type. Also as a consequence of the extirpation, large droplets were secreted in vacuoles of the organ of Bellonci. Neu-rosecretory cells in the medulla terminalis ganglionaris X organs (MTGX) showed increased activity and hypertrophy. The medulla externa X organ also had an impact on the distal retinal and chromatophoric red pigments. INTRODUCTION The eyestalks in decapod crustaceans are complex appendages considered to be the main source of hormones acting in several physiological and developmental processes. The anatomy and cytology of the nervous and neurosecretory structures of the optic ganglia, well known since Hanstrb'm's work (1928, 1947), have been described in numerous light-microscopic investigations. However, few studies deal with changes in the neurosecretory pathways of decapods after surgical interruptions. Several authors have been successful in removing the sinus gland in decapods (Brown, 1942; Scudamore, 1942; Panouse, 1944; Kleinholz, 1947; Stephens, 1951). But only Passano ( 1 95 1 a) and Bliss and Welsh (1952) observed changes so produced in eyestalk structures. Extirpation of the neurosecretory cell centers, carried out by Bliss and Welsh (1952) and by Passano (1953), gave a first idea of the histo-logical changes induced. Since then, no selective surgical experiments on the neu-rosecretory cell groups in the decapod eyestalk have been reported, although the removal of the organ of Bellonci and the medulla externa X organ (MEX) in the Natantia Palaemon serratus is technically possible (Pasteur, 1958). Our objective was to determine whether the chromatophore index and the blood Received 15 December 1979, accepted 24 November 1980. Abbreviations: CHH: Crustacean hyperglycemic hormone; DRPH: Distal retinal pigment hormone; MEX: Medulla externa X organ; MTGX 1 and 2: Medulla terminalis X organs 1 and 2; P.A.F.: Paraldehyde fuchsin; RPCH: Red pigment concentrating hormone. 1 Zoblogisch Laboratorium, Faculteit der Wiskunde en Natuurwetenschappen, Katholieke Uni-versiteit, Toernooiveld, 6525 ED Nijmegen, Nederland. 11
HISTOLOGICAL AND PHYSIOLOGICAL ASPECTS OF THE MEDULLA EXTERNA X ORGAN, A NEUROSECRETORY CELL GROUP IN THE EYESTALK OF PALAEMON SERRATUS PENNANT (CRUSTACEA, DECAPODA, NATANTIA)
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