The morphology of the cement gland apparatus of Larval Pterophyllum scalare Cuv. & Val. (Cichlidae,Teleostei)

Summary The cement gland apparatus of newly hatched Pterophyllum scalare Cuv. & Val. was examined by histology, scanning and transmission electron microscopy. The whole organ is composed of three pairs of endoepithelial, ductless glands, which cause prominent elevations on the larval head and are found in a specific arrangement. Each single gland is represented by an aggregation of elongated, tubular secretory cells surrounding a pyriform acinus. It overlies a basal lamina and is covered by the outer layer of the bilaminar embryonic epidermis.Two different types of secretory cells can be distinguished. One type is restricted to the bottom of the cavity. It is characterized by multiform cytoplasmic protrusions, which project into the gland's cavity. The secretory granules contain a network of light filamentous material. The second type constitutes the side wall of the acinus. It does not develop any protrusions. The contents of the secretory granules is of very high and homogeneous electron density. The mechanism of extrusion is discussed for both cell types. All secretory cells show a strong PAS-reaction. In SEM a circular microridge pattern with attached mucus globules can be recognized on the larval epithelial surface.Dedicated to Prof. Dr. H. Leonhardt on the occasion of his 60th birthday     

The human vocal cord surface

Summary The effect of phenylthiourea (PTU) on the pigment epithelium and the photoreceptor cells in the developing retina of Haplochromis burtoni was studied by electron microscopy. In the retinal pigment epithelium of 6-day old embryos, both types of melanin granule (spindle-shaped and rod-shaped) are already found. PTU inhibits the biosynthesis of melanin but does not influence the formation of premelanosomes so that in PTU-treated embryos there are no melanosomes, but an abundance of premelanosomes. The structure of the premelanosomes is described. It differs completely from that of all other vertebrates. Other changes: an increase in polysomes, retarded development of the inner segment of the photoreceptor cells and enlargement of the intercellular space between the inner and outer leaflet of the retina, may be due to a toxic effect of PTU.This investigation was supported by grants of the Deutsche Forschungsgemeinschaft     

Scanning electron microscopy of photoreceptor cells in the light- and dark-adapted retina of Haplochromis burtoni (Cichlidae,Teleostei)

Summary The photoreceptor layer in the retina of Haplochromis burtoni (Cichlidae, Teleostei) was studied by scanning electron microscopy. Three types of receptors were identified: rods, single-cones and double-cones. The three-dimensional arrangement of these photoreceptors is described in the light- and dark-adapted retina. The surface of the inner segment of the photoreceptor cells displays fine vertical fissures which give rise to slender processes. These so called calycal processes which are of different lengths in rods and cones, surround the beginning of the smooth-surfaced outer segment. The myoid, the contractile part of the receptor, which is located beneath the ellipsoid, was examined in the single-cones of the dark-adapted retina. It is a slender structure with surface infoldings. The myoid, studied by transmission electron microscopy, contains bundles of parallel myofilaments, which are thought to be contractile.This investigation was supported by grants of the Deutsche Forschungsgemeinschaft (Sonderforschungsbereich 51-E/10)