ALBERT

Notes: Summary 1. Providing the nest with vegetable food,Lethrus performs repeated excursions of about l m from the hole and returns home. 2. Homing by the straight line,Lethrus walks in compass direction toward the nest; the distance traveled is equal to the estimated distance to the hole, and in a case of faultLethrus begins the circling search.Lethrus is able to integrate over the complex path. 3. Lethrus sets direction relative to celestial cues: the sun and the polarized skylight. 4. Lethrus has two photoreceptor systems: the green-sensitive and UV-sensitive one; only an ultraviolet polarization pattern is used for polarotaxis. 5. The eye ofLethrus evolved from the superpositional prototype; it is adapted to diurnal vision by shortening of the clear zone and by thickening of the light-guiding tracts from the cone to the rhabdom. 6. Lethrus is different from other Lamellicorns possessing a typical multilobed rhabdom in thatLethrus has a crustacean-type rhabdom. It is assumed that this specialization of rhabdom provides the perfect analysis of polarized light and polarotaxis. 7. The complex orientational and nest behavior ofLethrus is not accompanied by enlargement of the brain and its presumed associative centres, the mushroom bodies. Among several scarabaeid beetles of comparable size (Amphimallon solstitialis, Geotrupes stercorosus)Lethrus apterus gains the first place in behavioral complexity but the last in number of sensilla on the antennal dumb, number of ommatidia, and the volume of mushroom globuli.

Notes: Summary Ultrastructural localization of potassium and calcium in the ommatidium of the house-cricketGryllus domeslicus L. was studied by X-ray microprobe analysis using samples prepared as thin sections (2 or 5 μm) of freeze-dried and embedded tissue. Real resolution was limited by the size of ice crystals (Fig. 2) and estimated as about 1 μm. Average values for potassium, calcium, sodium and phosphorus in different cells of the compound eye are given in Table 1. Striking non-uniformity in distribution of these elements over the cells and their compartments was found by probe scanning (Figs. 3, 4, 5). The highest potassium and calcium concentrations were measured in the pigmented zones of photoreceptors and pigment cells. The pigment granules are thought to be the ionic depots of the eye. Potassium and sodium are fully accessible to water in sections of embedded tissue, whereas all the calcium and half of the phosphorus are not. The functional significance of the non-uniformity discovered is briefly discussed.

Notes: Abstract The spectral sensitivity of 21 eye preparations of Ascalaphus (Libelluloides) macaronius (Insecta, Neuroptera) has been re-measured using an up-to-date spectral scan method. 1. Dorso-frontal and ventro-lateral eyes have different spectral characteristics with peaks of sensitivity at 329 ± 8 nm (n = 15) and 343 ± 4 nm (n = 5) (P = 0.002), respectively. 2. The absorbance of the visual pigment layer, K, determined from the shape of the spectral sensitivity curves is 1.3 ± 1.8(n = 15) for dorso-frontal eyes and − 1.0 ± 0.3(n = 5) for ventrolateral eyes, thus implying higher selfscreening in the dorso-frontal eyes and narrowing of the spectral sensitivity curves as regards to a template visual pigment in ventro-lateral eyes. 3. Plotting K versus spectral sensitivity peak wavelength λmax revealed an inverse correlation between these variables with K = 42.5 − 0.126 λmax at r = 0.88(n = 19). 4. Extracts of ommochromes and carotenoids (Figs. 4 to 6) do not allow to account for the above diversity of optical properties of the Ascalaphus eye (Fig. 7).

Notes: Abstract 1. The optics of the corneal facet lenses from the dorsal rim area (DRA) and from the dorso-lateral areas (DA) of the compound eye of the cricket Gryllus bimaculatus were studied. 2. The DRA of the cricket eye contains quite normally shaped facet lenses. The diameter of the facet lens in the DA is 2-fold larger compared to that in the DRA. The radius of curvature of the front surface is distinctly less in the DA facet lenses, as the surface of the facet lenses in the DRA are virtually flat. 3. The averaged axial refractive index of the facet lenses of Gryllus bimaculatus, measured by interference microscopy, was 1.496 ± 0.008 (n = 42) in the DRA and 1.469 ± 0.004 (n = 39) in the DA. The geometrical thickness of the lenses was calculated to be 77 ± 3 μm (n = 42) in the DRA and 56 ± 1 μm (n = 39) in the DA. 4. Analysis of the diffraction pattern obtained with a point light source revealed distinct focusing properties of both the DRA and the DA facet lenses; striking Airy-like diffraction patterns were obtained in both cases. 5. Focal distances measured directly at the backfocal plane were 40 ± 8 μm (n = 84) in the DRA of all the animals studied, and 60–90 μm (n = 62) in DA depending on the animal. Analysis of the diffraction of the point light source yielded very similar focal distances: 40 ± 5 μm (n = 10) in DRA and 81 ± 8 μm (n = 11) in DA. In the DRA, focal distance of the facet lenses was smaller than the cone length, 58 ± 3 μm (n = 9) while in the DA the focal distance matched the effective cone length, 71 ± 5 μm (n = 16).

Notes: Summary With the aim of clarifying the role of screening pigments in photoreceptor optics of the compound eye, a comparative study of the optical properties of the honeybee eye in the visible region of the spectrum was carried out using wild-type bees and eye colour mutantssnow, snow laranja, ivoryumberandchartreuse with total or partial blockage of the tryptophane-ommochrome pathway. 1. The electroretinogram (ERG) of mutant eyes displayed a sharp on-peak, this component being absent from normal heterozygote eyes (Fig. 6). 2. The ERG of newly emerged bees (a) lacked the above on-peak and showed oscillations in mutants, and (b) lacked the off-peak which always occurs in the ERG of adults in all the genotypes studied when stimulated by visible light. 3. The resting potentials of the receptor and cone cells were not found to be affected by mutations la, and the receptor potential ins/s ands la/slaphotoreceptors appeared to be similar to that in +/+ 4. Analysis of the amplitude characteristics of the whole eye of eight genotypes showed that the relative numbers of photons absorbed from an extended light source (4.5°×16.5°) and needed to elicit a standard ERG amplitude of 1 mV were as follows:s/s∶i u/iu∶sla/sla∶ch1/ch1∶(+/+; s/+ iu/+; sla/+)=1∶4.3∶8.6∶12.2∶(100–250). These ratios are believed to reflect the progress in ommochrome formation in these strains. 5. Spectral sensitivity curves (SSC) were obtained using an automatic spectrosensitometer and a spectral scan method which gave accurate results. The SSC of the whole eye in+/+ peaked at aλ max of 543±7 nm (SD,n=6), whereasλ max ins/s ands la/slashifted to 528±6 nm (n=9) and 548 ±3nm (n=6) respectively. The SSC ins/+ was the same as that in+/+. The bandwidth (width at 50% of peak sensitivity) of the SSC proved to be similar in+/+ ands/+ (126±10 nm and 128±8 nm), although ins/s the SSC appeared to be significantly narrower (106±7 nm;P〈0.01; Fig. 8, Table 2). 6. The peak spectral sensitivity of long-wave (LW) receptors lay at 541±5 nm (SD,n=14) in+/+ and at 526±5 nm (n=13) ins/s; the spectral distributions of the peaks in these genotypes were different. The bandwidth of the SSCs of the photoreceptors were 109±11 nm in+/+ and 103±4 nm ins/s, the difference being insignificant (Fig. 8, Table 2). The SSCs ins/s fit the absorption spectrum of pigment 526 (P 526) rather well whereas those in+/+ are noticeably distorted. The same is true for the whole-eye data. 7. A theory is advanced to account for the acceptance functions of the photoreceptors of eyes with imperfect pigmentation. Light scattering in imperfectly screened eyes was estimated using a factor which the termed we parasitic absorption coefficientp (see Theory). 8. The acceptance functions of LW photoreceptors were measured by three methods, and the results were similar to those predicted from the theory. On this basis the coefficientp was estimated; fors/s photoreceptors it lay between 0.65 and 0.76 according to experiments with a point light source (method 1), and was as great as 2.5 according to measurements with an extended light source (method 2). The latter technique, an integral method, made it possible to detect light scattering in normal bee eye, the coefficientp reaching 0.02 (Fig. 1, Table 3). 9. In genotypes+/+ ands la/slathe absorption spectra of screening pigments were recorded by microspectrophotometry (MSP), and greater transmission of red light than blue-green was found (Fig. 11). 10. Taking into account the screening effect of ommochromes, it is suggested that the visual pigment of LW photoreceptors in the honeybee eye is P 526; the absorption spectrum of this is highly similar to the SSC of LW photoreceptors in thes/s eye. 11. On the basis of our theory and experimental results, the contrast transfer function (CTF) for the white honeybee eye was estimated to be only 0.1 (for white and black patterns with the spatial wavelengthλ sp≫Δρ, the acceptance angle). Thus, the absence of screening pigments from the compound eye ofsnow mutants causes the great decrease in image contrast, and this serious sensory defect may be responsible for the fact that these mutants fail to find their way home.

Notes: [Auszug] My theory is based on some well known facts. Many insects have so-called tiered retinulas with one or more basal (or proximal) visual cells and both theoretical4 and experimental5*6 results indicate that the microvilli of rhabdomeres exhibit dichroism with a dichroic ratio of 2. Furthermore, ...

Notes: [Auszug] The retinula of the compound eye of the honey bee consists of eight (occasionally nine) visual cells6-8 which can be classified into three types according to their fine structure8. The arrangement of these cells within the retinula is shown in Figs. 1 and 2a. Colour vision in the honey bee is ...