Cuticular Photophores of Two Decapod Crustaceans, Oplophorus spinosus and Systellaspis debilis.

The organization, ultrastructure, growth, and development of two types of cuticular photophore in oplophorid shrimps (Oplophorus spinosus and Systellaspis debilis) are described. Photophores located in the third maxilliped consist of a unit structure comprising a single photocyte and associated pigment cells. Reflecting pigment cells contain white pigment and form an apical cap above the photocyte; sheath cells contain red carotenoid pigment and form a light-absorbing layer around the photophore. Photophores located on the pleopods are compound structures comprising many photocytes. They also contain the same types of pigment cell that are found in the unit photophores of the maxilliped. Paracrystalline bodies at the apical ends of the photocytes in both types of photophore are thought to be associated with light generation. Both types of photophore have mechanisms for tilting in the pitch plane. In the maxilliped, the apices of the photophores are connected to a ligament that has its origin in the propodus. Flexion or extension of the dactylus displaces the ligament, which tilts the photophores synchronously. The cuticular window beneath each photophore remains stationary. The tilt mechanism of the pleopod photophores is quite different, and depends upon muscular contraction. A main and an accessory longitudinal muscle cause backwards rotation of the photophore by deforming the cuticle surface. A loop muscle that passes around the anterior face of the photophore causes forward rotation. The two mechanisms optimize the use of the photophores in ventral camouflage. They allow photophore rotation to compensate for changes in the shrimp's orientation in the plane of pitch and thus maintain the ventral direction of the luminescence.

Formation of the retina-lamina projection of the cockroach: no evidence for neuronal specificity.

There is a topographical mapping of neural elements onto the lamina neuropile of the optic lobe of the cockroach, such that adjacent ommatidia project to adjacent points (optic cartridges) in the lamina neuropile. Postembryonic growth of the compound eye occurs by addition of new ommatidia to its growing margin. Retinula axons grow from the newly formed ommatidia to the lamina. By transplantation experiments in which the position or the orientation of retinal material is altered, it is shown that retinula axons do not make connections in the lamina with respect to their old position and orientation, but rather, in keeping with their new situations, apparently maintaining a retinotopic mapping upon the optic lobe.

Postembryonic growth of the compound eye of the cockroach.

The postembryonic growth of the compound eye of the cockroach Periplaneta americana involves increases in the size of the individual ommatidia as well as a 35-fold increase in the number of ommatidia. These ommatidia are added to the anterior, dorsal, and ventral margins of the eye by means of an almost continuous process of cell division in the proliferation zone in these margins. This proliferation phase is followed by a process of maturation of bundles of 'pre-ommatidial' cells into mature ommatidia, a process which involves further cell division. Processes involved in compound-eye development are investigated by eye margin grafting, histological techniques and cell proliferation studies.

A Golgi-electron-microscopical study of the structure and development of the lamina ganglionaris of the locust optic lobe.

The gross structure as well as the neuronal and non-neuronal components of the lamina ganglionaris of the locust Schistocerca gregaria are described on the basis of light- and electron-microscopical preparations of Golgi (selective silver) and ordinary histological preparations. The array of optic cartridges within the lamina neutropile--their order and arrangement--and the composition of the cartridges are described. There are six types of monopolar neurons: three whose branches reach to other cartridges and three whose branches are confined to their own cartridges. Retinula axons terminate either in the lamina or the medulla neuropiles. There are three types of centrifugal neurons, two types of horizontal neuron, as well as glia and trachea in the lamina neuropile. The development of the lamina neuropile is described in terms of developing monopolar and centrifugal axons, growing retinula fibres, and composition of the developing optic cartridges.

The eye margin and compound-eye development in the cockroach: evidence against recruitment.

The compound eye of the cockroach nymph grows from stadium to stadium by the addition of new ommatidia to the growing edge of the eye. By a series of transplant operations on Periplaneta americana and from SEM studies on Gromphadorhina portentosa it is shown that the proliferating region of the eye margin is a budding zone. There is no recruitment of larval head-capsule epidermis into the eye.

Ommatidium assembly and formation of the retina-lamina projection in interspecific chimeras of cockroach.

By grafting operations, interspecific eye chimeras of the cockroaches Gromphadorhina portentosa and Leucophaea maderae were produced. Mechanisms involved the development of both the compound eye and the retina-lamina projection have been studied. Most cell types composing the eyes of these cockroaches are cytologically distinguishable in the chimera; also, retinula axons forming the retina-lamina projection in the two species are of vastly different lengths. At the border between host and graft eye tissue, individual ommatidia are formed containing cells of both types. It particular, it is shown that the four cone cells can be found in any of the possible combinations of the two cell types. This shows that the cone cells within one ommatidium are not necessarily related by lineage. These results are in agreement with the hypothesis that cells within an ommatidium are determined by position rather than by a lineage mechanism. Furthermore, formation of mosaic ommatidia suggests that mechanisms governing eye formation are similar in these two species. The formation of the projection from donor retina to host lamina shows that axon elongation is not rigidly programmed, but that the axons grow until they reach a suitable target at which point connexions are made.

The ultrastructure of implanted trophoblast cells of the yellow agouti mouse.

An electron microscope study of ultrathin sections of trophoblast cells of implanting blastocysts resulting from the crossing of heterozygous yellow agouti mice has been conducted. Several conditions for successful preparation of the blastocysts have been described. These include avoidance of the use of sucrose in the buffers, reduction of specimen washing times and exclusion of propylene oxide from the dehydration procedure. Electron micrographs of cells from a blastocyst considered, on the basis of light microscopy, to be 'abnormal' revealed a cytoplasm with many 'empty' areas and numerous 'vacuolated' mitochondria. Electron micrographs of cells from blastocysts considered to be 'normal' revealed, in one instance, a preponderance of cells with very few of these 'abnormal' features, and, in the other instance, a preponderance of cells with many abnormalities. Both 'normal' blastocysts revealed cellular features usually regarded as either primitive or pathological, namely tight junctions, vacuolated mitochondria and mitochondria with cristae oriented parallel to their long axis. It was generally concluded that the appearance of the blastocysts, in the light microscope, at 100-105 hours of development, could not be used as a valid criterion of normality or abnormality, for, although a blastocyst classified as 'abnormal' under the light microscope appeared 'abnormal' also in the electron microscope, those classified as 'normal' under the light microscope appeared either 'normal' or 'abnormal' in the electron microscope. This disturbing situation may indicate that the electron microscope is diagnosing 'abnormality' before the light microscope. The presence of immature forms of organelles (e.g., vacuolated mitochondria) indicates either a failure to mature or regression. Failure to mature could be benign or of sinister import.