The compound eye of<Emphasis Type="Italic"> Scutigera coleoptrata</Emphasis> (Linnaeus, 1758) (Chilopoda: Notostigmophora): an ultrastructural reinvestigation that adds support to the Mandibulata concept

The lateral compound eye of Scutigera coleoptrata was examined by electron microscopy. Each ommatidium consists of a dioptric apparatus, formed by a cornea and a multipartite eucone crystalline cone, a bilayered retinula and a surrounding sheath of primary pigment and interommatidial pigment cells. With reference to the median eye region, each cone is made up of eight cone segments belonging to four cone cells. The nuclei of the cone cells are located proximally outside the cone near the transition area between distal and proximal retinula cells. The connection between nuclear region and cone segment is via a narrow cytoplasmic strand, which splits into two distal cytoplasmic processes. Additionally, from the nuclear region of each cone cell a single cytoplasmic process runs in a proximal direction to the basement membrane. The bilayered rhabdom is usually made up of the rhabdomeres of 9–12 distal retinula cells and four proximal retinula cell. The pigment shield is composed of primary pigment cells (which most likely secrete the corneal lens) and interommatidial pigment cells. The primary pigment cells underlie the cornea and surround, more or less, the upper third of the crystalline cone. By giving rise to the cornea and by functioning as part of the pigment shield these pigment cells serve a double function. Interommatidial pigment cells extend from the cornea to the basement membrane and stabilise the ommatidium. In particular, the presence of cone cells, primary pigment cells as well as interommatidial pigment cells in the compound eye of S. coleoptrata is seen as an important morphological support for the Mandibulata concept. Furthermore, the phylogenetic significance of these cell types is discussed with respect to the Tetraconata.     

Do retinula cells trigger the screening pigment migration in the eye of the mothEphestia kuehniella?

Summary Simultaneous recordings of reflectance and the electroretinogram (ERG) of the meal moth superposition eye show a good match between the action spectrum of screening pigment migration and the spectral sensitivity curve (Fig. 5). These spectra correspond with the absorption spectrum of a xanthopsin X530 that has been evidenced in the eye. No correlation was found with the extinction spectrum of the pigment granules themselves (Fig. 7). The results suggest, that the photomechanical reaction is controlled by the visual pigment.     

Retinal receptor types inAglais urticae andPieris brassicae (Lepidoptera), revealed by analysis of the electroretinogram obtained with Fourier interferometric stimulation (FIS)

Summary Electroretinograms obtained in the butterfliesAglais urticae andPieris brassicae by the procedure of Fourier interferometric stimulation (FIS) were used to construct spectral sensitivity curves. These curves, representing the combined responses of several receptor types, were approximated by summation of spectral sensitivity curves for individual pigments, and the presence of these pigments was corroborated by chromatic adaptation experiments. The results show that the retina in the compound eye ofAglais urticae contains 3 photopigments, with maximal absorption at ca. 360 nm, 460 nm and 530 nm, respectively (Fig. 5). The retina in the compound eye ofPieris brassicae has two subdivisions. In the dorsal region of the eye 3 photopigments were found, with maxima at ca. 360 nm, 450 nm and 560 nm (Fig. 8). In the medioventral region pigments with essentially the same maxima are present together with an additional, fourth long-wavelength component with effective maximal absorption at ca. 620 nm (Fig. 11). Its absorption curve is considerably narrower than would be expected for a rhodopsin with the same absorption maximum, and presumably results from the spectral combination of a photopigment and a photostable screening pigment.Abbreviations FIS Fourier interferometric stimulation - WLP White-light position - ERG Electroretinogram     

Fine structure of light- and dark-adapted eyes of desert ants,Cataglyphis bicolor (Formicidae,Hymenoptera)

Among ants, Cataglyphis bicolor shows the best performance in optical orientation. Its eye is of the apposition type with a fused rhabdom. Morphological studies on the general struture of the eye as well as the effect of light have been carried out with transmission and scanning electron microscopy. An ommatidium is composed of a dioptric apparatus, consisting of a cornea, corneal process and a crystalline cone, the sensory retinula, which is made up of eight retinula cells in the distal half and of an additional ninth one in the proximal half. The ommatidia are separated from each other by two primary pigment cells, which surround the crystalline cone and an average of 12 secondary pigment cells, which reach from cornea to the basement membrane. The eye of Cataglyphis bicolor possesses a light intensity dependent adaptation mechanism, which causes a radial and distal movement of the pigment granules within the retinula cells and a dilatation of cisternae of the ER along the rhabdom. Until now, no overall order in arrangement of retinula cells or direction of microvilli has been found from ommatidium to ommatidium. Such an order, however, must exist, either on the retina or the lamina level, since we have proven the ant's capacity for polarized light analysis.     

Structure,histochemistry, ontogenetic development,and regeneration of the ocellus of Cladonema radiatum dujardin (cnidaria,hydrozoa, anthomedusae)

The ectodermal eyes, 45–55 μm in diameter, of the cnidarian hydrozoan Cladonema radiatum Dujardin possess a lens approximately 15 μm in diameter enveloped by an eyecup (retina). An overlying layer of intensely vacuolated distal process of the adjoining epithelial cells forms a transparent cornea. The eyecup is composed of three cell types: basal cells, melanin-containing pigment cells, and photoreceptor cells. The last two cell types occur in the ratio of approximately 2:1. Histogenesis of the eye both during ontogeny and regeneration is described from light and electron microscopic investigations. During ontogeny the cell types forming the retina are derived from a compact group of morphologically undifferentiated cells, but during regeneration a primordium is formed by regeneration cells. In both cases the lens is built from distal nonnucleated cytoplasmic portions pinched off from the pigment cells. The cornea is formed by distal lamellar processes of the ocellus adjoining the epithelial cells. Through EM-histochemical methods (silver impregnation and DOPA-oxidase reaction) the pigment of the chromatophores of the retina was identified as melanin.     

Le contrôle automatique du flux lumineux dans l'oeil composé des Diptères

In the compound eye of the fly Musca, tiny pigment granules move within the cytoplasm of receptor cells Nos. 1–6 and cluster along the wall of the rhabdomeres under light adaptation, thus attenuating the light flux to which the visual pigment is exposed (Kirschfeld and Franceschini, 1969). Two recently developed optical methods (the neutralization of the cornea and the deep pseudopupil) combined with antidromic and orthodromic illumination of the eye (Fig. 1) make it possible to analyse the properties of the mechanism at the level of the single cell, in live and intact insects (Drosophila and Musca). The mechanism is shown to be an efficient attenuator in the spectral range (blue-green) where cells Nos. 1–6 have been reported to be maximally sensitive (Figs. 4c and d, 5b and 11b). In spite of the fact that the granules do not penetrate into the rhabdomere, the attenuation spectrum they bring about closely matches the absorption spectrum of the substance of which they are composed (ommochrome pigment, dotted curve in Fig. 11b). The dramatic increase in reflectance of the receptors after light adaptation (Figs. 3, 4b, 5a and 11a) can be explained as a mere by-product of the high absorption index of the ommochrome pigment, especially if one takes into account the phenomenon of anomalous dispersion (Chapter 8). The vivid green or yellow colour of the rhabdomeres would thus have a physical origin comparable to a metallic glint. Contrasting with the lens eye in which the pupillary mechanism is a common attenuator for both receptor types (rods and cones), the compound eye of higher Diptera is equiped with two types of pupils adapted respectively to both visual subsystems. A scotopic pupil is present in each of the six cells (Nos. 1–6) whose signals are gathered in a common cartridge of the first optic ganglion. This pupil comes into play at a moderate luminance (0,3 cd/m² in Drosophila; 3 to 10 cd/m² in Musca. Figs 13, 14, 15, 16). A photopic pupil is present in the central cell No. 7 whose signal reaches one column of the second optic ganglion. Attenuating the light flux for both central cells 7 and 8, the photopic pupil has its threshold about two decades higher than the scotopic pupil, just at the point where the latter reaches saturation (Fig. 3b, e-State II of Figs. 6b and 15). The photopic pupil itself saturates at a luminance one to two decades higher still (Fig. 3c, f=State III of Figs. 6c and 15). The two-decades-shift in threshold of these pupil-mechanisms supports the view that receptors 1–6 are a scotopic subsystem, receptors 7 and 8 a photopic subsystem of the dipteran eye. The luminance-threshold of the scotopic pupil (as determined with the apparatus described in Fig. 2) appears to be located at least 3.5 decades (Drosophila) or even 5 decades (Musca) higher than the absolute threshold of movement perception (Fig. 16). After a long period (1 hr) of darkness a light step of high intensity can close the scotopic pupil within about 10 sec (time constant 2 sec as in Fig. 9) and the photopic pupil within no less than 30–60 sec. Some mutants of Drosophila possess only a scotopic pupil (w , Figs. 4 and 5) whereas ommochrome deficient mutants lack both types of pupil (v, cn, see Fig. 7c, d). Comparable reflectance changes, accomplished within about 60 sec of light adaptation, are described for two insects having fused rhabdomes: the bee and the locust (Fig. 17).     

Photoreceptor-specific efficiencies of β-carotene,zeaxanthin and lutein for photopigment formation deduced from receptor mutant Drosophila melanogaster

Summary Drosophila rearing media had only -carotene, zeaxanthin or lutein as precursors for photopigment chromophores. Zeaxanthin and lutein are potentially optimum sources of the 3-hydroxylated retinoids of visual and accessory photopigments. Mutants made the electroretinogram in white (w) eyes selective for compound eye photoreceptors R1–6, R7 and R8: R1–6 domiantes w's electroretinogram; R7/8 generates w;ora's (ora = outer rhabdomeres absent); R8 generates w sev;- ora's (sev = sevenless). Microspectrophotometry revealed R1-6's visual pigment. In w, all 3 carotenoids yielded monotonic dose-responses for sensitivity (Fig. 4) or visual pigment (Fig. 7). An ultraviolet sensitivity peak from R1-6's sensitizing pigment was present at high but not low doses (Fig. 1). In w;ora, all 3 carotenoids gave similar spectra dominated by R7's high ultraviolet sensitivity (Fig. 2). For w sev;ora, all spectra were the shape expected for R8, peaking around 510 nm (Fig. 3). The sensitivity dose-response was at its ceiling except for low doses in w;ora (Fig. 5) and zero supplementation in w sev;ora (Fig. 6). Hence, without R1-6, most of our dose range mediated maximal visual pigment formation. In Drosophila, -carotene, zeaxanthin and lutein mediate the formation of all major photopigments in R1-6, R7 and R8.Abbreviations ERG electroretinogram - MSP microspectrophotometry - HPLC high pressure liquid chromatography - n.a. numerical aperture - w, sev, ora Drosophila mutants - y, p, r marg types of R7 and R8     

Theory and Measurement of the buffer value of bicarbonate in saliva

All known sensory systems have at least two components, which will tend to counteract and compensate for each other. For light, the sensitivity of the eye is some function of the area of the pupil (aperture of the iris diaphragm) and the relative amount of unbleached pigment (visual purple or rhodopsin). An intermittent light will result in a constriction of the pupil and a bleaching of the pigment. The interaction between these two processes results in a total response with components of both a logarithmic and an arithmetic function of the light intensity and duration. The sensitivity of the eye is a linear function of the logarithm of the intensity of incident light (Weber's and Fechner's laws, Fig. 6), yet a rapidly oscillating light causes approximately the same sensitivity as a steady light of the same intensity as the arithmetic average of the fluctuating light (Talbot's and Bloch's laws, Fig. 9c).     

Ultrastructure of the eye of the amber snail Succinea putris (L.) (Gastropoda, Stylommatophora)]

The structure and some aspects of the development of the eye of Succinea putris were studied with the aid of the electron microscope. The eye is of the closed vesicle type and is composed of retina, cornea, vitreous body, lens and optic nerve. Three different types of cell are to be found in the retina: (1) the small elongated pigment cell with an avoid nucleus, many pigment granulae and short microvilli at the apical end of the cell; (2) the sensory cell type I with a large irregular nucleus, long microvilli, which extend to under the surface of the lens, a large number of light-cored vesicles, 700 A in diameter and the axon; (3) the elongated slender sensory cell type II with many dense cored vesicles, several pigment granulae in the distal region of the cell and short irregular microvilli at the apical end of the cell. This type is few in number. Two results of the study of the embryonic eye are described: the cornea cells differ from those in the adult eye in the nucleus-cytoplasm relation and the optic nerve is smaller than in the adult eye.     

The pigment system of the photoreceptor 7 yellow in the fly,a complex photoreceptor

Summary The 7y photoreceptor in the fly (Musca, Calliphora) retina harbours an unusually complex pigment system consisting of a bistable visual pigment (xanthopsin, X and metaxanthopsin, M), a blue-absorbing C₄₀-carotenoid (zeaxanthin and/or lutein) and a uv sensitizing pigment (3-OH retinol).The difference spectrum and photoequilibrium spectrum in single 7y rhabdomeres were determined microspectrophotometrically (Fig. 2).The extinction spectrum of the C₄₀-carotenoid has a pronounced vibrational structure, with peaks at 430, 450 and 480 nm (Fig. 3). The off-axis spectral sensitivity, determined electrophysiologically with 1 nm resolution shows no trace of this fine structure thus excluding the possibility that the C₄₀-carotenoid is a second sensitizing pigment (Fig. 4).The absorption spectra of X and M are derived by fitting nomogram spectra (based on fly R1–6 xanthopsin) to the difference spectrum. max for X is 425 nm, and for M 510 nm (Fig. 5). It is shown that the photoequilibrium spectrum and the difference spectrum can be used to derive the relative photosensitivity spectra of X and M using the analytical method developed by Stavenga (1975). The result (Fig. 6) shows a pronounced uv sensitivity for both, X and M, indicating that the uv sensitizing pigment transfers energy to both X and M. A value of 0.7 for, the relative efficiency of photoconversion for X and M, is obtained by fitting the analytically derived relative photosensitivity spectra to the absorption spectra at wavelengths beyond 420 nm.     

鳜皮肤图案中色素细胞的分布与排列

色素细胞是皮肤图案形成的基础,为了解鳜(Siniperca chuatsi)皮肤图案区域色素细胞的种类、分布及排列特征,采用光学显微镜与电子显微镜对鳜皮肤中图案区域、非图案区域及交界处皮肤的色素细胞进行显微及超显微结构观察。结果显示,鳜皮肤中含有黑色素细胞、黄色素细胞、红色素细胞及虹彩细胞,主要分布于表皮层和色素层。头部过眼条纹、躯干纵带、躯干斑块等图案区域皮肤表皮层与色素层均含有黑色素细胞,非图案区域仅表皮层含有少量黑色素细胞。躯干图案区域(纵带、斑块)皮肤色素层色素细胞分布层次明显,由外到内依次为黄色素细胞、红色素细胞、黑色素细胞和虹彩细胞,其中,虹彩细胞内反射小板较长,整齐水平排列;躯干非图案区域皮肤色素层由外到内依次为黄色素细胞、红色素细胞和虹彩细胞,其中,虹彩细胞内反射小板较短,无规则排列。头部过眼条纹色素层含有4种色素细胞,色素细胞数量较少,且无规则排列,其中,黑色素细胞内黑色素颗粒较大。交界处皮肤色素层黑色素细胞数量向非图案区域一侧逐渐减少,虹彩细胞数量逐渐增加。结果表明,鳜图案区域与非图案区域、不同图案区域的色素细胞分布与排列各不相同,本研究结果为鳜色素细胞图案化形成机...     

Elementary detectors for vertical movement in the visual system of Drosophila

Optomotor thrust responses of the fruitfly Drosophila melanogaster to moving gratings have been analysed in order to determine the arrangement of elementary movement detectors in the hexagonal array of the compound eye. These detectors enable the fly to perceive vertical movement. The results indicate that, under photopic stimulation of a lateral equatorial eye region, the movement specific response originates predominantly from two types of elementary movement detectors which connect neighbouring visual elements in the compound eye. One of the detectors is oriented vertically, the other detector deviates 60° towards the anterior-superior direction (Fig. 5b). The maximum of the thrust differences to antagonistic movement is obtained if the pattern is moving vertically or along a superior/anterior — inferior/posterior direction 30° displaced from the vertical (Fig. 3d,e, Fig. 6). Only one of the detectors coincides with one of the two detectors responsible for horizontal movement detection. This indicates that a third movement specific interaction in the compound eye of Drosophila has to be postulated. — The contrast dependence of the thrust response (Fig. 2) yields the acceptance angle of the receptors mediating the response. The result coincides with the acceptance angle found by analysis of the turning response of Drosophila (Heisenberg and Buchner, 1977). This value corresponds to the acceptance angle expected, on the basis of optical considerations, for the receptor system R 1–6. — The movement-specific neuronal network responsible for thrust control is not homogeneous throughout the visual field of Drosophila. Magnitude and preferred direction of the thrust response in the upper frontal part of the visual field seem to vary considerably in different flies (Fig. 6).     

The larval eye of the aeolid nudibranch Trinchesia aurantia (Alder and Hancock)

Summary The larval eye of the aeolid nudibranch Trinchesia aurantia has been investigated at three different stages; in all, the eyes remain closely attached to, and in cellular contact with, the central ganglia. The larval eye is a simplified version of the adult eye in that, the eye and the constituent cells, nuclei, lens, microvilli and pigment granules are all smaller, and the interdigitation between the retinal cells is not developed. The absence of the small cells of the cornea and of the spherical vesicles in the cytoplasm of the sensory cells, is further evidence of the incomplete formation of the eye. The possible origin of the eye of Trinchesia is discussed and compared with that of other gastropods.I am very grateful for the help and guidance of my supervisor Dr. D. A. Dorsett throughout the preparation of this paper. I was sponsored by a grant from the N.E.R.C.     

The lateral line mechanoreceptive mesencephalic,diencephalic, and telencephalic regions in the thornback ray,Platyrhinoidis triseriata (Elasmobranchii)

Central lateral line pathways were mapped in the thronback ray, Platyrhinoidis triseriata, by analyzing depth profiles of averaged evoked potentials (AEPs), multiunit activity (MUA), and single unit recordings. Neural activity evoked by contra- or ipsilateral posterior lateral line nerve (pLLN) shock is restricted to the tectum mesencephali, the dorsomedial nucleus (DMN) and anterior nucleus (AN) of the mesencephalic nuclear complex, the posterior central thalamic nucleus (PCT), the lateral tuberal nucleus of the hypothalamus, and the deep medial pallium of the telencephalon (Figs. 2, 3, 4, 6, 7). Neural responses (AEPs and MUA) recorded in different lateral line areas differ with respect to shape, dynamic response properties, and/or latencies (Figs. 9, 10 and Table 1). Ipsilaterally recorded mesencephalic and diencephalic AEPs are less pronounced and of longer latency than their contralateral counterpart (Fig. 9 and Table 1). In contrast, AEP recorded in the telencephalon show a weak ipsilateral preference. If stimulated with a low amplitude water wave most DMN, AN, and tectal lateral line units respond in the frequency range 6.5 Hz to 200 Hz. Best frequencies (in terms of least displacement) are 75-150 Hz with a peak-to-peak water displacement of 0.04 micron sufficient to evoke a response in the most sensitive units (Fig. 11A, B, C). DMN and AN lateral line units have small excitatory receptive fields (RFs). Anterior, middle, and posterior body surfaces map onto the rostral, middle, and posterior brain surfaces of the contralateral DMN (Fig. 12). Some units recorded in the PCT are bimodal; they respond to a hydrodynamic flow field--generated with a ruler approaching the fish--only if the light is on and the eye facing the ruler is left uncovered (Fig. 13).     

Post-embryonic photoreceptor development and dark/light adaptation in the spittle bug Philaenus spumarius (L.) (Homoptera, Cercopidae)

The aims of this paper have been to describe (1) the general structure of the compound eye of the spittle bug Philaenus spumarius, (2) the eye's post-embryonic development, (3) photomechanical changes upon dark/light adaptation in the eye, and (4) how leaving the semi-aquatic foam bubble and turning into an adult affects the organization of the eye. Spittle bugs, irrespective of size or sex, possess apposition type compound eyes. The eye's major components (i.e. facet, cornea, cone and rhabdom) grow rather isometrically from the smallest nymph to the adult. Photomechanical changes can occur during both nymphal and adult phases and manifest themselves through pigment granules and mitochondria migrating to and away from the rhabdom, and rhabdom diameters varying with time of day and ambient light level. When a nymph transforms into an adult, its compound eyes’ dorsoventral axes widen, facet diameters increase, facet shapes turn from circular to pentagonal and hexagonal, the cornea thickens and the rhabdoms become thinner. The agile adults, free from the foam that surrounds the nymphs, can be expected to need their vision more than the nymphs, and the changes in eye structure do, indeed, indicate that the adults have superior visual acuity. A thicker cornea in the adults reduces water loss and protects the compound eye from mechanical and light-induced damage: protection given to the nymphs by their foam bubbles.     

南五台蝎蛉成虫复眼的超微结构

采用扫描电镜和组织切片法,观察南五台蝎蛉Panorpa nanwutaina Chou成虫复眼的超微结构。南五台蝎蛉复眼近半椭球形,包括1500～1600个小眼。小眼表面光滑,由角膜、晶体、2个初级和12个次级色素细胞、视杆、以及基膜组成。角膜为多层片状纤维结构;晶体含有4个晶锥细胞;视杆由若干个视网膜细胞组成。晶体、视杆周围、和色素细胞内含有大量的色素颗粒,基膜两侧也有色素颗粒分布。南五台蝎蛉的复眼属于并列像眼。与普通蝎蛉P.communis L.小眼的次级色素细胞数目不同。讨论了南五台蝎蛉角膜的功能以及感觉毛和次级色素细胞在分类中的作用。     

灰茶尺蠖成虫复眼的超微结构及其明暗适应中的变化

【目的】明确灰茶尺蠖Ectropis grisescens成虫复眼的超微结构及其明暗适应中的变化,探究其调光机制。【方法】采用超景深显微镜测定了灰茶尺蠖成虫复眼的小眼数量、间角、直径和曲率半径等外部参数,并通过组织切片、光学显微镜和透射电子显微镜等技术观察了复眼的内部超微结构;通过光学显微镜观察了灰茶尺蠖成虫复眼在明暗环境中分别适应2 h后晶锥结构及色素颗粒的位置变化。【结果】灰茶尺蠖成虫复眼呈半球形,雌、雄虫单个复眼分别有2 502±105和3 123±78个小眼。小眼自远端至近端由角膜、晶锥、透明区构成的屈光层和由15个视网膜细胞构成的感光层组成。2个初级色素细胞包裹着晶锥,自角膜近端延伸至视网膜细胞核区的远端;每个小眼外围由6个次级色素细胞围绕,自角膜近端延伸至基膜;在透明区内14个视网膜细胞聚集成束(非感杆束),远端与晶锥束末端连接,在感光层内形成闭合型感杆束,延伸至第15个视网膜细胞(基部视网膜细胞)。在明暗适应时,灰茶尺蠖复眼的晶锥细胞间出现开闭,色素颗粒进行纵向位移,以适应外界的光强度的变化。【结论】灰茶尺蠖成虫复眼属于重叠像眼,感杆束为“14+1”模式;屏蔽色素颗粒的移...     

Spectral sensitivities of retinular cells measured in intact,living flies by an optical method

Summary The spectral sensitivity of the peripheral retinular cells R1–6 in nine species of intact flies was determined using non-invasive, optical measurements of the increase in reflectance that accompanies the pupillary response. Our technique is to chronically illuminate a localized region of the eye with a long wavelength beam, adjusted to bring pupillary scattering above threshold, then, after stabilization, to stimulate with monochromatic flashes. A criterion increase in scattering is achieved at each wavelength by adjusting flash intensity. Univariance of the pupillary response is demonstrated by Fig. 3.Action spectra measured with this optical method are essentially the same as the published spectral sensitivity functions measured with intracellular electrophysiological methods (Fig. 4 forCalliphora, Fig. 5 forDrosophila, Fig. 7 forEristalis, and Fig. 8 forMusca). This holds for both the long wavelength peak and the high sensitivity in the UV as was consistently found in all investigated fly species.Spectral sensitivity functions for R1–6 of hover flies (family Syrphidae) are quite different in different regions of the same eye. There can also be substantial differences between the two sexes of the same species. The ventral pole of the eye of femaleAllograpta (Fig. 10) contains receptors with a major peak at 450 nm, similar to those ofEristalis. However, the dorsal pole of the same eye contains receptors with a major peak at 495 nm, similar to those ofCalliphom. Both dorsal and ventral regions of the maleToxomerus eye, and the ventral region of the female eye, contain only the 450 nm type of R1-6 (see Fig. 12). However, the dorsal region of the female eye also contains another spectral type of receptor that is maximally sensitive at long wavelength. Eyes of both sexes ofAllograpta (Figs. 10 and 11) contain a mixture of spectral types of receptors R1-6.We thank Dr. Chris Maier of the Connecticut Agricultural Experiment Station, for determination of the Syrphidae. This work was supported by grants EY01140 and EY00785 from the National Eye Institute, U.S.P.H.S., (to GDB), by the Connecticut Lions Eye Research Foundation (to GDB), and by the Netherlands Organization for the Advancement of Pure Research (Z.W.O.), (to DGS).     

Preparation of Adult Drosophila Eyes for Thin Sectioning and Microscopic Analysis

Drosophila has long been used as model system to study development, mainly due to the ease with which it is genetically tractable. Over the years, a plethora of mutant strains and technical tricks have been developed to allow sophisticated questions to be asked and answered in a reasonable amount of time. Fundamental insight into the interplay of components of all known major signaling pathways has been obtained in forward and reverse genetic Drosophila studies. The fly eye has proven to be exceptionally well suited for mutational analysis, since, under laboratory conditions, flies can survive without functional eyes. Furthermore, the surface of the insect eye is composed of some 800 individual unit eyes (facets or ommatidia) that form a regular, smooth surface when looked at under a dissecting microscope. Thus, it is easy to see whether a mutation might affect eye development or growth by externally looking for the loss of the smooth surface (''rough eye'' phenotype; Fig. 1) or overall eye size, respectively (for examples of screens based on external eye morphology see e.g.¹). Subsequent detailed analyses of eye phenotypes require fixation, plastic embedding and thin-sectioning of adult eyes.The Drosophila eye develops from the so-called eye imaginal disc, a bag of epithelial cells that proliferate and differentiate during larval and pupal stages (for review see e.g. ²). Each ommatidium consists of 20 cells, including eight photoreceptors (PR or R-cells; Fig. 2), four lens-secreting cone cells, pigment cells (''hexagon'' around R-cell cluster) and a bristle. The photoreceptors of each ommatidium, most easily identified by their light sensitive organelles, the rhabdomeres, are organized in a trapezoid made up of the six "outer" (R1-6) and two "inner" photoreceptors (R7/8; R8 [Fig. 2] is underneath R7 and thus only seen in sections from deeper areas of the eye). The trapezoid of each facet is precisely aligned with those of its neighbors and the overall anteroposterior and dorsoventral axes of the eye (Fig. 3A). In particular, the ommatidia of the dorsal and ventral (black and red arrows, respectively) halves of the eye are mirror images of each other and correspond to two chiral forms established during planar cell polarity signaling (for review see e.g. ³).The method to generate semi-thin eye sections (such as those presented in Fig. 3) described here is slightly modified from the one originally described by Tomlinson and Ready⁴. It allows the morphological analysis of all cells except for the transparent cone cells. In addition, the pigment of R-cells (blue arrowheads in Fig. 2 and 3) can be used as a cell-autonomous marker for the genotype of a R-cell, thus genetic requirements of genes in a subset of R-cells can readily be determined^5,6.     

Pore canals in the cornea of a functionally specialized area of the honey bee's compound eye

Summary The fine structure of the cornea in an anatomically and functionally specialized part of the honey bee's compound eye (dorsal rim area) was examined by light microscopy, transmission electron and scanning electron microscopy. Under incident illumination the cornea appears grey and cloudy, leaving only the centers of the corneal lenses clear. This is due to numerous pore canals that penetrate the cornea from the inside, ending a few m below the outer surface. They consist of (1) a small cylindrical cellular evagination of a pigment cell (proximal), and (2) a rugged-walled, pinetree-shaped extracellular part (distal). The functional significance of these pore canals is discussed. It is concluded that their light scattering properties cause the wide visual fields of the photoreceptor cells measured electrophysiologically in the dorsal rim area, and that this is related to the way this eye region detects polarization in skylight.