Microtubules in the epidermal cells of Carausius morosus (Br.). Their pattern and relation to pigment migration

The existence of one or several systems of microtubules, consisting of a central bundle that branches off towards the basal and distal ends of epidermal cells of Carausius morosus has been shown by indirect immuno-fluorescence microscopy using monospecific anti-tubulin. The pattern of microtubules coincides with the position of the ommochrome granules and their migration path during physiological colour change. The ommochrome granules stick to isolated bundles of microtubules. Small bundles of microtubules extend almost perpendicularly towards the apical cell membrane where they are attached. Distally they are covered by pore channels within the cuticle. Parallel to the basal cell membrane and in close contact with it, there are very small bundles of microtubules. These findings strongly support the idea that during physiological colour change the ommochrome granules migrate along a firmly fixed system of microtubules.     

Colour and colour change in the grasshopper, Kosciuscola tristis

The males of the small grasshopper (Kosciuscola tristis), with a restricted range above 1830 m in the Australian Alps, exhibit a remarkable colour change. They are dark, almost black, when cold and change to a bright sky blue colour within minutes of exposure to warmth.Sections of cuticle fixed in the two conditions confirm that the cells underlying the cuticle contain two kinds of granules: large (diameter 1·0 μm) spherical, brown granules, and smaller (0·17 μm) less dense granules. In the blue (warm) condition the small granules are closely packed in the distal part of the cells, whereas the ‘black’ granules are found predominantly in the deeper proximal zones. Evidence is presented to suggest that the blue colour arises from Tyndall scattering of light by the suspension of small granules and is intensified by being seen against a dark background.In the black condition the black granules are found to have moved towards the surface, mingling with the smaller granules and ‘quenching’ the light scattering.The smaller granules are white in the isolated state. They consist of a mixture of uric acid and a pteridine, probably leucopterin.The epidermal cells contain numerous microtubules, which are directed towards the cell surface, that is, parallel to the direction of movement of the granules. It is possible that the microtubules are associated with the movement.     

Physiological colour changes in Odonata eyes. A comparison between eye and epidermal chromatophore pigment migrations

Pigment migration in the eyes of Austrolestes annulosus and Ischnura heterosticta cause pronounced colour changes which superficially resemble those of Odonata epidermal chromatophores. In both species, the migratory pigment is confined to the distal pigment cells of dorsal ommatidia. When the pigment is concentrated around the base of the crystalline cones, a dense layer of Tyndall blue bodies produce bright ‘blue phase’ colours. Distal migration of the pigment disrupts the Tyndall effect and produces ‘dark phase’ (grey-brown) colours. As in chromatophores, eye pigments consist of a mixture of xanthommatin and dihydroxanthommatin together with an additional pigment, possibly ommin A, not found in chromatophores.As with chromatophores, eye pigments respond to change in temperature only, change in light intensity having no effect. The change from blue to dark phase (at 8°C) occurs at the same rate as in chromatophores, whereas the reverse change (at 20°C) is significantly slower. Equilibrium colours at constant temperature are variable but significantly different from those of chromatophores at 12°C and above. There is no diurnal variation in responsiveness as is found in chromatophores.Isolated dark phase eyes or undamaged pieces of eye are able to change to blue phase after temperature increase. Isolated blue phase eyes show little response to temperature decrease, isolated undamaged pieces show no response. A temperature difference between the eyes of the same intact insect may result in minor colour differences. Ablation of the optic tract or of tissue posterior to the optic tract prevents normal colour change from blue to dark phase. The above results indicate that eye pigment cells are structurally similar to Odonata chromatophores and are under similar environmental and physiological control.     

Histochemical localization of Mg2+-activated ATPases on microtubule bundles in epidermal cells of Carausius morosus: Possible significance to pigment migration

We have demonstrated the presence of Mg²⁺-stimulated ATPases on microtubule bundles in the epidermal cells at the light microscope level, using specific histochemical techniques. This method provides an alternative method to immunohistochemistry for identifying microtubule bundles in the epidermal cells of Carausius morosus using the light microscope. The close association between ommochrome granules and the microtubule bundles support the hypothesis, that these ATPases play an important role in force generation, required to move ommochrome granules during physiological colour change.     

Body Colouration Related to the Deposition of Pteridines in the Epidermis and Other Organs of Dysdercus Species (Insecta; Heteroptera: Pyrrhocoridae)

In epidermal cells of Dysdercus species, two types of pigment granules were detected using both light and electron microscopic methods; the granules differed in colour, size, distribution and osmiophily. Red (D. intermedius) and yellow (D. nigrofasciatus) epidermal cells contained both types of granules, but in white cells only one type was present. Chromatographic analyses showed that the larger granules were more transparent to electrons, and contained uric acid, while the smaller ones contained erythropterin, became coloured later, and were osmiophilic. In accordance with these findings, in the testes of D. intermedius both granule types were present, but in the testes of D. nigrofasciatus only those containing erythropterin. The number of granules per cell varied with the species and developmental stage. Epidermal cells of D. intermedius contained more erythropterin granules than those of D. nigrofasciatus, the reverse occurring in the testes. This pattern corresponded to the visible colouration of the insects. As the development progressed, a decrease of the red and an increase of the white granules took place in the coloured epidermal cells. The main amount of pteridines, except isoxanthopterin, was accumulated in the integument of the insects studied. Chemical and histological data showed the influence of pterins on insect colouration. Orange, yellow and red colours were caused by different amounts of erythropterin containing special granules in the epidermal cells, and the white colour only by uric acid containing granules. A partial melanization of the cuticle resulted in dark spots below which pteridines were deposited additionally in the epidermal cells. Considering erythropterin, the quantitative chemical data are in accordance with the histological ones and also with the colouration externally visible. Intensively red coloured stages had a higher concentration of erythropterin and more corresponding granules than the light-red coloured ones; the lowest amount was found in yellow coloured insects. Therefore, the pigmentation effect of erythropterin, which reached from yellow to orange and red, depended on its concentration and played the most important role in the colouration of the Dysdercus species studied, uric acid was responsible for the colouration of the white parts of the integument.     

Identification of two types of melanocyte within the stria vascularis of the mouse inner ear

We have distinguished two types of melanocyte within the intermediate layer of the stria vascularis in the cochlea of normally pigmented mice: light and dark intermediate cells. The light intermediate cells are present in the stria from birth and have the typical appearance of a melanocyte. They are large and dendritic with electron-lucent cytoplasm containing numerous vesicles that show tyrosinase activity, and pigment granules in various stages of development. These granules have the ultrastructural and histochemical characteristics of premelanosomes and melanosomes. The light intermediate cells persist throughout life, but less frequently contain pigment in older animals. The dark intermediate cells, present only in adult mice, vary considerably in number and distribution between animals. Pigment granules, bound within an electron-dense acid phosphatase-rich matrix, form the main component of the dark intermediate cells. The intermediate cells may comprise either two distinct cell populations or different developmental stages of the same cell type; ultrastructural observations suggest the latter. In young mice, light intermediate cells contain the electron-dense matrices, which at later stages of development are found almost exclusively in dark cells. The dark intermediate cells contain few cell organelles other than pigment granules accumulated within lysosomal bodies and they often have pycnotic nuclei. These observations suggest that the dark intermediate cells are a degenerate form of the light intermediate cells. Clusters of melanosomes also occur in the basal cells, and to a much lesser extent in the marginal cells. These cells do not stain after incubation in DOPA, suggesting that they are not capable of melanin synthesis, and therefore probably acquire melanin by donation from adjacent melanocytes. Pigment clusters are also found within the spiral ligament at all stages of development.     

Coloring cells of the cornea of trout]

Cells from the eye cornea of Hexagrammos octagrammus which are responsible for changes of the cornea colour from bright orange to colourless, depending on the light conditions, are described. It was shown that the change in cornea colour was due to a shift of red pigment from the cell body into its processes (in the light) and in the opposite direction at the dark adaptation of animals. The ultrastructural constitution of these cells has a number of characteristics. The whole cell cytoplasm is filled up with fine lipid droplets wherein carotenoid pigments giving red colour to these cells are presumably dissolved; the cytoplasmic membrane forms numerous deep and branched folds into the cell and has a lot of pinocytose visicles; the cell body and especially the process display many microtubes arranged regularly. The described cells differ greatly in their form, size and ultrastructural constitution from the known types of pigment cells (melanophores, xanthophores and erythrophores). This makes it possible to consider them as chromatophores of an independent type.     

The effect of light-dark adaptation on the ultrastructure ofLimulus lateral eye retinular cells

Summary The fine structure of retinular cells within lateral eyes ofLimulus polyphemus which had been dark or light adapted for 12 h in vivo was studied via electron microscopy. The ommatidium to ommatidium and retinular cell to retinular cell variability observed in light microscope studies was confirmed. The rhabdomeric microvilli were longer and narrower, the area of contiguous microvillar membranes greater, the endoplasmic reticulum less abundant and the mitochondrial granules (? calcium containing) more numerous in well dark adapted than in well light adapted retinular cells (Figs. 1, 3, 4, 7, 8) and membrane whorls or vacuoles were present in the peripheral cytoplasm of very well light adapted retinular cells (Fig. 6). Phagocytotic vesicles, multivesicular bodies and lysosomes were present in the interrhabdomeral cytoplasm of partially light adapted retinular cells (Figs. 1, 2, 3, 10). The number of retinular cell microvilli in contact with the eccentric cell dendrite was smaller in very well light adapted than in well dark adapted ommatidia (Fig. 9). The possible functional significance of these light-dependent structural changes is discussed.This investigation was supported in part by Grant 2 RO1 EY 00236 National Eye Institute, National Institutes of HealthMember of the SFB 160 of the Deutsche Forschungsgemeinschaft     

大草蛉成虫复眼的外部形态及其显微结构

用扫描电镜和光学显微镜观察了大草蛉Chrysopa pallens Ramber成虫复眼的外部形态及明、暗适应和性别对其显微结构的影响。结果发现：（1）其复眼呈半球形,位于头部两侧,略成“八”字形排列,单个复眼约由3 600个小眼组成,最前和最后小眼之间的夹角约为180°,最上和最下小眼之间的夹角约200°;（2）小眼主要由角膜、晶锥和6～8个小网膜细胞、基膜组成,外围环绕有2个初级虹膜色素细胞和6个次级虹膜色素细胞,基膜处有色素颗粒分布;（3）暗适应时,晶锥开裂程度较大,远端5～7个网膜细胞核向远端移动,与晶锥近端相接或接近,次级虹膜色素颗粒亦向远端移动包围晶锥;明适应时,晶锥开裂程度小或闭合,远端网膜细胞核向近端移动,透明带显现,大部分次级虹膜色素颗粒亦向近端移动分布在小网膜细胞柱周围,包被透明带;（4）在相同的明、暗适应下,雌、雄成虫复眼的显微结构无明显差异。结果表明大草蛉复眼为透明带明显的重叠象眼,其小眼不但具有次级虹膜色素颗粒纵向移动的常规调光机制,还存在晶锥开闭、远端网膜细胞核移动和基膜色素颗粒纵向扩散的调光新机制。     

Hell-und Dunkeladaptation der Augen vonPieris brassicae L. (Lepidoptera)

Summary The compound eyes ofPieris brassicae L. have a tiered retina. During light and dark adaptation, ultrastructural changes have been observed throughout the length of the ommatidia in the latero-ventral region of the eyes. These changes have been quantitated by mapping at distinct levels of the ommatidia, and plotted as histograms. Both in visual cells and secondary pigment cells and at the attachment region between crystalline cone and rhabdome such ultrastructural changes have been found to be correlated to the state of adaptation.Distal and proximal photoreceptor cells show different adaptation mechanisms. Whereas the distal cells show a clear pupil mechanism in their distal parts, there is only very little horizontal movement of pigment granules in the proximal cells. In the proximal cells, multivesicular bodies (MVB) are always abundant, while in the distal cells their number is small and increases slightly during light adaptation. In the proximal cells light adaptation causes pigment granules, located in the distal process, to move proximally. Increasing the light intensity from 160 to 1600 W/cm² results in more intense migration of pigments.In the secondary pigment cells, a slight but significant distal movement of pigment granules is observed at high light intensity. If continued this condition causes the granules to aggregate in the vicinity of the apical cell membrane, and to move up to the distal inflated extensions of the distal processes formed by these cells. In dark adapted eyes, these processes are nearly devoid of pigment and the pigment granules beneath the apical membrane disperse. In addition to these structural changes, there is a tendency for retinal movements at the attachment from crystalline cone to rhabdome. — The various adaptation mechanisms are not equally well developed in different regions of the compound eye.

---

Hell-und Dunkeladaptation der Augen vonPieris brassicae L. (Lepidoptera)

Zusammenfassung Die Retina vonPieris brassicae L. ist mehrreihig. Erstmals wurden feinstrukturelle Veränderungen während der Hell und Dunkeladaptation über die gesamte Länge der Ommatidien des latero-ventralen Augenbereichs anhand von Kartierungen in vergleichbaren Höhen der Ommatidien untersucht und in Histogrammen wiedergegeben. — Sowohl in den Sehzellen als auch Nebenpigmentzellen und am Übergang von Kristallkegel zum Rhabdom wurden feinstrukturelle Veränderungen in Korrelation mit der Adaptation gefunden.Die Adaptation erfolgt bei distalen und proximalen Sehzellen jeweils auf andere Art. Während die distalen Sehzellen in ihrem distalsten Bereich sehr gut die Pupillenreaktion zeigen, adaptieren die proximalen Sehzellen nur geringfügig mit horizontaler Pigmentwanderung. Auch die Anzahl der multivesikulären Körper (MVB), die in den proximalen Sehzellen immer groß ist, steigt bei Helladaptation (HA) nur in den distalen Sehzellen etwas an. In den proximalen Sehzellen wandern die Pigmentgranula bei HA geringfügig aus dem distalen Fortsatz dieser Sehzellen proximalwärts. Intensitätssteigerung auf das 10fache (von 160 auf 1600W/cm²) bewirkt eine Verstärkung der genannten Pigmentwanderungs-Reaktionen in den Sehzellen.Die Granula der Nebenpigmentzellen wandern bei HA mit starker Intensität etwas distalwärts. — Bei starker langer HA häufen sich diese Granula unter der apikalen Membran dieser Nebenpigmentzellen und wandern bis in die distalen kleinen Erweiterungen der distalen Fortsätze dieser Zellen. Bei Dunkeladaptation (DA) sind diese Fortsätze nahezu frei von Pigment; unter der apikalen Zellmembran verteilen sich die Pigmente locker. Außerdem besteht am Übergang von Kristallkegel zu Rhabdom die Tendenz zur Retinomotorik. — In den verschiedenen Augenbereichen erfolgen die genannten Adaptationsreaktionen unterschiedlich gut.

---

---

Mit Unterstützung der Deutschen Forschungsgemeinschaft und der Stiftung Volkswagenwerk

---

Herrn Prof. Dr. Kurt Hamdorf (Bochum) danken wir für kritische Diskussion und Fräulein Althaus für die graphischen Darstellungen     

Insect pupil mechanisms

Summary The hypothesis that the glow observable in dark adapted butterfly eyes is extinguished upon light adaptation by the action of migrating retinula cell pigment granules (Stavenga, 1975a) has been investigated. Experimental procedures applying optical methods to intact, living animals were similar to those used previously to investigate the migration of retinula cell pigment granules in Hymenoptera (Stavenga and Kuiper, 1977). The data obtained from nymphalid butterflies and Hymenoptera show close parallels, favouring the pigment migration hypothesis.The retinula cell pigment granules control the light flux in the butterfly rhabdom and hence are part of a pupil mechanism. The range of action of this pupil mechanism is about 3 log units of light intensity. The speed of pupil closure is slowed down with longer dark adaptation times. The way in which pupil processes can be distinguished from photochemical processes of the visual pigment is discussed.     

Immunocytochemical localization of epidermal growth factor in mouse submandibular gland.

The cellular and subcellular localization of epidermal growth factor in the submandibular glands of male and female adult mice was established by immunoperoxidase techniques. In light microscopic preparations epidermal growth factor was found exclusively in the granular convoluted tubules of the gland. The intensity of staining for epidermal growth factor varied from cell to cell, and some cells apparently were negative. The pattern of staining was similar in the glands of male and female mice; however, the granular convoluted tubules are androgen-responsive, and thus more extensive and composed of larger cells in males. In thin sections epidermal growth factor was most heavily concentrated in the secretion granules of the granular convoluted tubule cells. Within a given cell there was variation in intensity of staining of individual secretion granules, with some granules appearing minimally reactive or negative. The only other cell component with deposits of reaction product was the ribosomes.     

飞蝗复眼生理和结构上的节律变化

采用细胞内记录和光镜方法研究了飞蝗(Locusta migratoria)夜间和日间在暗适应和明适应状态下小网膜细胞角敏感度以及晶锥和小网膜细胞之间区域结构上的变化.结果表明小网膜细胞角敏感度的变化不仅仅由于晶锥周围主色素细胞色素颗粒的移动,而且也由于小眼感杆束结构上的节律变化.     

Zur Ultrastruktur der phaeochromen Zellen im Nebennierenmark der Ratte

Zusammenfassung Das Nebennierenmark der Ratte wurde vergleichend licht- und elektronenoptisch unter verschiedenen Bedingungen untersucht. Die nach phaeochromer Reaktion im Lichtmikroskop sichtbaren hellen und dunklen Markzellen lassen sich anhand ihrer cytoplasmatischen Granula bei geeigneter Technik ultrastrukturell als zwei differente Zellsysteme identifizieren. Die Morphologie der Granula einerseits und das unterschiedliche Verhalten der beiden Zellsysteme nach Insulinapplikation andererseits erlauben, unter Heranziehung vor allem biochemischer Ergebnisse, den Schluß, daß der helle Zelltyp (I) vorwiegend oder ausschließlich Adrenalin, der dunkle Zelltyp (II) entsprechend Noradrenalin enthält. Diese Typisierung scheint auch für die phaeochromen Zellen des Nebennierenmarks anderer Tierspecies gültig zu sein. Es werden ferner die Faktoren diskutiert, welche bei der Darstellbarkeit der beiden phaeochromen Granulumtypen im Elektronenmikroskop eine Rolle spielen dürften.

---

Summary The chromaffin cells of the adrenal medulla of the rat were investigated by light and electron microscopy on the resting animal and after insulin treatment. With adequate techniques, the light and dark cells visible in the light microscope after chromaffin reaction can be identified in the electron microscope, by their cytoplasmic granules, as two different cell types. The morphologic classification of the granules and the different reaction of the two cell types following the injection of insulin, under consideration of the biochemical, physiological and pharmacological findings, lead to the conclusion that the light cells (I) mainly or exclusively contain epinephrine; the same applies, as concerning norepinephrine, to the dark cells (II). This classification appears to apply also to the chromaffin cells of the adrenal medulla of other animal species. Furthermore, the factors are discussed which influence the visualization and the differentiation of the two types of chromaffin granules.

---

---

Arbeit mit Unterstützung durch den Schweizerischen Nationalfonds und die Forschungs-kommission der Universität Basel.     

The ontogeny of facultative superposition optics in a shrimp eye: hatching through metamorphosis

Summary Compound eyes of larval and first postlarval grass shrimp (Palaemonetes pugio Holthuis) were studied with light and electron microscopy following adaptation to darkness or bright light. Larvae have well-developed apposition eyes, including 3 main types of accessory screening and reflecting pigments and a fourth class of putatively reflective granules recently described in adult shrimps. Rhabdoms contain orthogonally layered microvilli, and by the last larval stage, 8 retinular cells. Ocular accessory pigments in both light- and dark-adapted larvae are distributed much like those of light-adapted adults, but the distal mass of reflecting pigment is concentrated dorsally in larvae and ventrally in adults. Since larvae swim upside-down, reflecting pigment is oriented downward in all developmental stages and may function for countershading. Light and dark adaptational migrations of all 3 major accessory pigments commence abruptly at metamorphosis to the first postlarva. Upon dark adaptation in postlarvae, superposition optics remain impossible because (1) distal screening pigment migrates only slightly, (2) no clear zone has developed, and (3) the crystalline cones remain circular in cross section. Nevertheless, a slight improvement in photon catch is expected due to extensive redistributions of reflecting pigment and retinular cell screening pigment granules.

---

     

Ultrastructure of the tubular nephron of the lizard Podarcis (= Lacerta) Taurica

The proximal, intermediate, and distal convoluted tubules of the neprhon of Podarcis (= Lacerta) taurica were examined by electron microscopy. Proximal tubule cells have large, apical cytoplasmic protrusions and microvilli interpreted to function in urate secretion. Adjacent cells are bound apically by tight junctions and desmosomes but interdigitate in their basal region. This situation is repeated in the other tubules with significant differences in intercellular space width. The basal surfaces bear numerous cytoplasmic processes. The intermediate tubule has proximal and distal segments each with dark, ciliated, and light cells, the cuboidal dark cells with dense cytoplasm constituting the main bulk of the wall. As the cells of the proximal and distal segments resemble those of the proximal and distal convoluted tubules, respectively, the intermediate tubule is considered as a transition region. The ciliated cell body has two broad processes extending from the lumen, one to the basement membrane and one to a foot process of a light cell. The light cell is surrounded by dark and ciliated cells. It does not reach the lumen, but contacts the basement membrane through a process running below a ciliated cell to form a mushroom-shaped structure in tubule cross-section, the light cell process forming the stalk and a ciliated cell the cap. The cilia probably propel the glomerular filtrate towards the distal convoluted tubule. This latter tubule has initial, middle, and terminal zones, all nonciliated but with different lumen widths and cell shapes.     

钙离子浓度对暗适应时的中华绒螯蟹光感受器超微结构的影响

用透射电镜研究了暗适应时中华绒螯蟹的光感受器超微结构与外界钙离子浓度的关系,结果显示出与培育在生理溶液中的光感受器相比,细胞外钙离子浓度升高,使得感杆束的直径急剧缩小,感杆束周围胞质增厚,胞饮泡增加,膜下猪泡囊极度减小。胞质中多囊体的数量和直径减小,而板模体和溶酶体的数量增加,同时细胞内的色素颗粒增多。分布在小网膜细胞的远端。细胞的结构表现为类似光适应状态,与之相反,细胞外钙离子浓度降低时小眼的感     

The Fine Structure of Nerve Cells and Fibers, Neuroglia, and Sheaths of the Ganglion Chain in the Cockroach (Periplaneta americana)

The abdominal nerve cord of Periplaneta americana was studied utilizing light and electron microscopes. In the nerve cells, delicate granules, similar to those probably responsible for cytoplasmic basophilia, are evenly distributed in "dark" cells and clumped in "light" cells. Neuroglial cells are stained metachromatically by cresyl violet. The neuroglial cells have many processes which ramify extensively and are enmeshed to form overlapping layers. These imbricated processes ensheath the nerve cells; the inner layer of the sheath penetrates into the neuron and is responsible for the appearance of the trophospongium of Holmgren. Nerve fibers are embedded within glial cells and surrounded by extensions of the plasma membrane similar to mesaxons. Depending on their size, two or several nerve fibers may share a single glial cell. Nerve fibers near their terminations on other nerve fibers contain particles and numerous, large mitochondria. The ganglion is ensheathed by a thick feltwork of connective tissue and perilemmal cells. The abdominal connective has a thinner connective tissue sheath which is without perilemmal cells. The nerve fibers and sheaths in the connective become thinner as they pass through ganglia.     

How and why do plant nuclei move in response to light?

We recently found that nuclei take different intracellular positions depending upon dark and light conditions in Arabidopsis thaliana leaf cells. Under dark conditions, nuclei in both epidermal and mesophyll cells are distributed baso-centrally within the cell (dark position). Under light conditions, in contrast, nuclei are distributed along the anticlinal walls (light position). Nuclear repositioning from the dark to light positions is induced specifically by blue light at >50 µmol m⁻² s⁻¹ in a reversible manner. Using analysis of mutant plants, it was demonstrated that the response is mediated by the blue-light photoreceptor phototropin2. Intriguingly, phototropin2 also seems to play an important role in the proper positioning of nuclei and chloroplasts under dark conditions. Light-dependent nuclear positioning is one of the organelle movements regulated by phototropin2. However, the mechanisms of organelle motility, physiological significance, and generality of the phenomenon are poorly understood. In this addendum, we discussed how and why nuclei move depending on light, together with future perspectives.Key words: actin, Arabidopsis, blue light, cytoskeleton, nuclear positioning, nucleus, phototropin     

Turnover of pigment granules: Cyclic catabolism and anabolism of ommochromes within epidermal cells

Ommochromes are end products of the tryptophan metabolism in arthropods. While the anabolism of ommochromes has been well studied, the catabolism is totally unknown. In order to study it, we used the crab-spider Misumena vatia, which is able to change color reversibly in a few days, from yellow to white and back. Ommochromes is the only pigment class responsible for the body coloration in this animal. The aim of this study was to analyze the fine structure of the epidermal cells in bleaching spiders, in an attempt to correlate morphological changes with the fate of the pigment granules. Central to the process of bleaching is the lysis of the ommochrome granules. In the same cell, intact granules and granules in different degradation stages are found. The degradation begins with granule autolysis. Some components are extruded in the extracellular space and others are recycled via autophagy. Abundant glycogen appears associated to granulolysis. In a later stage of bleaching, ommochrome progranules, typical of white spiders, appear in the distal zone of the same epidermal cell. Catabolism and anabolism of pigment granules thus take place simultaneously in spider epidermal cells. A cyclic pathway of pigment granules formation and degradation, throughout a complete cycle of color change is proposed, together with an explanation for this turnover, involving photoprotection against UV by ommochromes metabolites. The presence of this turnover for melanins is discussed.