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Notes: Summary 1. Azimuth orientation in the halfbeak fishDermogenys was studied in the laboratory to find out whether its spontaneous heading directions in a vertical beam of linearly polarized light involve perception of thee-vectorper se or merely of concomitant light intensity patterns. Responses were tested with polarized and unpolarized light as well as with either a uniform white screen horizontally surrounding the experimental vessel or with one divided into black and white alternating quadrants. 2. Measured as counts within 10 °, 45 ° or 90 ° sectors through 180 ° the fish's azimuth orientation was random with unpolarized light and the white surround (Fig. 2). 3. In contrast significant preferential orientation was shown in the presence of linearly polarized light and the white surround (Fig. 3). The 10 ° sector centered on the plane of vibration had the most counts (Fig. 3A). Combining the data into four sectors each 45 ° in extent makes clear a significant predominance of orientation parallel to thee-vector (Fig. 3B) as do the total counts for parallel and perpendicular quadrants (Fig. 3D). 4. With the black and white quadrants combined with unpolarized light preferential orientation was clearly shown toward the light sectors (Fig. 4A, B). Since maximum differential scattering from a linearly polarized light beam is perpendicular to the plane of vibration the positive sign of this phototactic response ofDermogenys is evidence that the observed orientation parallel to thee-vector cannot also be a similar response to intensity pattern. Hence the plane of vibration must be perceived through a distinct information channel and polarotaxis is different from phototaxis. 5. Tests with linear polarized light combined with the black and white surround proved that phototaxis predominated over polarotaxis under our experimental conditions and that the interaction between the two types of behavior in this case was not a simple additive one (Fig. 4C-F).

Notes: Summary 1. Because behavioral evidence indicates that fishes can perceivee-vector direction in plane polarized light, intracellular recordings were made on bipolar cells, ganglion cells, amacrine cells and horizontal cells in the goldfish retina. In flattened retinal fragments stimulated with polarized flashes no evidence for significante-vector sensitivities was found. 2. Dichroism could not be demonstrated in the cornea, lens or other dioptric elements of this fish eye. 3. Finally extracellular spike recordings of single units in the goldfish optic tectum were made to determine whethere-vector discrimination could be measured in the output of the intact eye in the living fish. 500 msec test flashes were presented to the retina with narrow band spectral red, green and blue light (quantum equalized) as well as with white light over a 4–5 log unit range of intensities. 4. Practically all tectal cells of the 47 successfully recorded showed some sensitivity toe-vector direction. The response function was roughly sinusoidal with maxima and minima 90° apart. Maximal responses to polarization plane orientation were found in all sixe-vector directions tested. Consequently an analyzer without discrete channels for particular polarization planes must be present quite different from that present in many rhabdom bearing eyes. 5. E-vector direction influenced various parameters of the tectal responses (on, off, sustained, etc.) in some cases in the same direction and in other cases in the opposite direction. Both excitatory and inhibitory components, as well as color coded ones, were affected. 6. Intensity response curves indicate polarized light sensitivity ratios ranging from 1.4 to 31.7, with a mean of 8.2 for 13 cases.

Notes: Summary 1. Spike responses of single optic tectal units to plane polarized light have been recorded with extracellular electrodes in the goldfish. Responses to a series of eight 500 msec flashes were summed and the quantitative effects ofe-vector direction studied over 4–5 log units of intensity with white light and narrow spectral bands of equal quantal content at 460, 540 and 620 nm. 2. As previously reported all or nearly all tectal cells tested (115) were sensitive to the direction of the stimulus' polarization plane. Control experiments with a thin high order birefringent retarder next to the cornea and acting as a pseudo depolarizer provided further proof that thee-vector discrimination found in the optic tectum (as well as the previously reported oriented behavior to polarized light in fish) depends on an intraocular analyzer. 3. Systematic study of tectal cells has been made at various depths and in all directly accessible areas. No localized or differential effects of recording depth one-vector discrimination have been found. However, both directions of maximum response and degree of polarized light sensitivity (PLS) show distinctive patterns over the tectal area. 4. On the basis of established tectal projection maps these data show that preferred retinale-vector directions are tangentially arranged around the eye axis when the stimulus is axial. Distribution of this angular sensitivity seems continuous without discrete channels favoring particular polarization planes. 5. Sensitivity (determined from intensity response curves) is minimal in the center of the retina for an axial stimulus and increases peripherally out to 50–60° or more off axis. Sensitivity ratios of 4–6 are common and much larger ones have been occasionally recorded. 6. Shifting the direction of stimulus from axial to 45° and 60° upward from the axis proved that retinal patterns of preferrede-vector directions and sensitivities are symmetrical relative to the beam axis rather than the anatomical eye axis. Therefore individual tectal cells and before them their retinal receptor elements show different directions ofe-vector preference and different PLS ratios depending on the stimulus configuration. 7. Intensity response curves determined with the red, green and blue narrow spectral bands were essentially superimposable. Therefore, we have no evidence that there is any special interaction of λ and PLS. 8. The effects of stimulus intensity and retinal adaptation on the IR curves do not indicate any particular selective effects. Substantial polarized light sensitivity was present in both the light adapted and dark adapted state. PLS ratios in various cases were (1) about the same at different intensity levels or (2) greater at low than high intensities or (3) greater at high than low intensities. 9. We conclude that linearly polarized light evokes a large entoptic image in the goldfish eye. Two opposite light sectors perpendicular to thee-vector alternate with two dark sectors parallel to thee-vector. Both Haidinger's brushes and Boehm's brushes in human vision show some similarities but also some important differences. The goldfish PL image is achromatic, weak or absent axially and strong peripherally. Also the contrast between the sectors does not depend on movement of the stimulus on the retina to prevent fading as it does in both of the other phenomena. 10. The most likely mechanism for the observed PLS in the goldfish eye is either differential scattering intraocularly or oblique entry of light into the receptor outer segments. Yet present data prevent a firm choice between them.

Notes: [Auszug] Nevertheless, there are actually three previous reports of polarized light responses by teleost fishes3-5, but none of these was adequately followed up to provide needed additional data or reasonable explanations for certain ambiguous or anomalous experimental results. We now report consistent ...

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Notes: Summary 1. Fine structural effects of longterm continuous darkness (2–16 weeks) have been quantitatively measured in five rhabdom parameters of adult crayfish (Procambarus) using transmission (Figs. 3–6) and freeze fracture (Figs. 13–15) electron micrographs. The most striking modifications took place during the first four weeks. 2. During the first two weeks in darkness four changes occurred: a) the diameter of rhabdom microvilli increased significantly (Figs. 9, 10), b) the diameter of particles (one or more rhodopsin molecules) visualized on the protoplasmic face of the receptor membrane by freeze fracture (Figs. 13–15) decreased significantly, whereas c) their number increased (Fig. 16) and d) lysosome related bodies near the rhabdom (Figs. 3, 4) in all five retinular regions studied strongly decreased in number (Fig. 12). 3. During weeks 3 and 4 in darkness two further changes occurred: a) the normally regular microvillus pattern of the photoreceptor membrane (Figs. 1, 2) was significantly disrupted and b) the number of membrane particles then fell to about half their initial count (Fig. 16) except in retinular cell eight where they maintained control levels for up to two months in the dark. 4. Most of these effects of prolonged darkness have clear functional implications. Disruption of microvillus pattern and sustained decrease in visual pigment concentration after more than two weeks without light reflect deterioration in vision. Alterations in microvillus diameters and lysosome density imply changes in the membrane turnover steady state resulting from protracted darkness. The data demonstrate that normal photoreceptor membrane could not be maintained in this eye for long in the absence of light. 5. The dark-induced disorganization of microvillus regularity confirms the earlier, disputed demonstration but also shows regional differences in susceptibility which might explain different conclusions drawn from local samples. 6. New distinctive features of retinular cell eight were found in its minimal sensitivity to microvillus disruption compared with the seven regular retinular cells and its maintenance of control densities of membrane particles despite two months continuous darkness.

Notes: Summary 1. Two decapod cephalopoda, Euprymna (a sepiolid) and Sepioteuthis (a squid) have been tested for their orientation behavior in a vertical beam of linearly polarized light and in horizontal light intensity patterns. 2. Like many arthropods these mollusks show four preferential swimming directions relative to the e-vector (0°, 90° and ±45°) 3. Horizontal intensity patterns induce only positive or positive and negative phototactic orientation. 4. When polarized light and intensity patterns are presented together the polarized light response predominates. 5. Polarized light vision in these decapod mollusks is a distinct perceptual process showing remarkable convergence wiht this function in arthropods.

Notes: Zusammenfassung 1. Die Krabbe Ocypode ceratophthalma (Pallas) lebt im Sand der Gezeitenzone tropischer und subtropischer Meere im Indo-Pazifischen Raum. Die Jungtiere graben schräg nach unten führende Gänge, die sie zur Nahrungsaufnahme verlassen und wieder aufsuchen. Mit ihnen wurden in Hawaii Versuche über Vorhandensein, Art und Mechanismus einer Orientierung nach polarisiertem Licht durchgeführt. 2. Die Jungtiere (und die Postmegalopastadien) stellen Körperachsen und Laufrichtung unter künstlich polarisiertem Licht in der Dunkelkammer in konstanten Winkeln senkrecht, parallel und ± 45° diagonal zur Schwingungsrichtung ein und zwar sowohl in der Luft als auch unter Wasser (achtsinnige-Grundorientierung Fig. 3, S. 59). Dasselbe Verhalten zeigen die Tiere in zwei verschiedenen Versuchsanordnungen auch unter dem natürlich polarisiertem Himmelslicht im Zenit (Fig. 7, S. 65 und Fig. 9a, S. 67). In einem Falle lief eine Krabbe, der 2 Beine fehlten, ausschließlich senkrecht zur Schwingungsrichtung im Zenit (zweisinnige Grundorientierung Fig. 9b, S. 67). 3. Der Mechanismus zur Analyse der Schwingungsrichtung arbeitet unabhängig von dem Mechanismus der Lichtmuster analysiert. 4. Auch im unpolarisierten Licht besitzt die Krabbe 8 Vorzugslaufrichtungen relativ zur Körperachse, die sich um 45° unterscheiden. Mehr als die Hälfte der Läufe erfolgt quer zur Körperachse (Fig. 5, S. 61). 5. Unter den gegebenen Versuchsbedingungen war keine Korrelation zwischen einer Stellung der Körperachse relativ zur Schwingungsrichtung einerseits und einer Stellung der Körperachse relativ zur Laufrichtung andererseits festzustellen. Bei jeder Einstellung der Körperachse zur Schwingungsrichtung traten die Vorzugslaufrichtungen relativ zur Körperachse in konstanter Häufigkeit auf. 6. Energiegleiches polarisiertes und nicht polarisiertes Licht erscheinen den Krabben gleich hell. 7. Die Tiere haben in der Versuchsanordnung unter dem Polarisationsmuster des blauen Himmels nicht die Kompaßrichtung Land-Meer eingeschlagen. 8. Die Tiere orientieren sich nach wiederholten spontanen Läufen von ihrem Schlupfloch zu einem Köder auf dem Rückweg menotaktisch nach dem Polarisationsmuster des blauen Himmels.

Notes: Zusammenfassung 1. Daphnia schødleri zeigt selbst in mehrfach gefiltertem Wasser starke Richtungsorientierung in der Horizontalebene, wenn von oben linear polarisiertes Licht einfällt. Eine mäßige Verbesserung des Orientierungsgrades erreicht man durch trüben des Wassers mit Hefepulver. 2. Mysidium gracile orientierte sich in entsprechenden Experimenten in gefiltertem Wasser schwächer als Daphnia jedoch noch signifikant (S. 166). Hefepulver im Wasser erhöht den Orientierungsgrad von Mysidium 2–3 mal stärker als von Daphnia. Diese Verbesserung muß ein optischer Effekt sein, da die Mysideen in einem Doppelgefäß von dem trüben Medium isoliert waren. 3. Versuche mit Mysideen in verschiedenartigen trüben Medien zeigen, daß die Trübung nicht nur durch die optische Dichte auf die Orientierungsleistung wirkt, sondern auch durch das Intensitätsverhältnis des gestreuten Lichtes quer und parallel zur Polarisationsebene. Eine kolloidale Suspension von Siliziumdioxyd mit hohem Trübungsgrad und erheblichen Intensitätsunterschieden im horizontalen Streulicht erhöht merklich den Orientierungsgrad. In Versuchen mit starker Trübung aber geringen Intensitätsunterschieden im Streulicht ist ein zweiter Orientierungsgipfel angedeutet. Der höchste mit Mysidium gefundene Orientierungsgrad im trüben Medium ist deutlich geringer als der von Daphnia in klar gefiltertem Wasser. 4. Die Angaben über die Orientierung der beiden Krebsarten beschreiben quantitativ die Wechselwirkungen zwischen dem polarisierten Licht und dem horizontalen Streulichtmuster. Starke Orientierung in gefiltertem Wasser legt nahe, beweist jedoch nicht, daß am Orientierungsvorgang zwei getrennte Sinnesmechanismen beteiligt sind (S. 169). 5. Aus den Versuchen folgt, daß Einzeltiere von Daphnia und Mysidium meistens asymmetrisch auf Reizung durch polarisiertes Licht reagieren. Die orientierten Tiere können bis zu 30° von der Richtung quer zur Polarisationsebene abweichen. Betrag und Seite der Abweichung eines Tieres kann sich ändern. Es ist möglich, daß es sich hier um eine echte menotaktische Orientierung handelt.

Notes: Summary 1. Effects of light and dark adaptation on the photoreceptor membranes of the rock crabGrapsus have been quantitatively studied using light and electron microscopy to document changes in rhabdom size and their fine structural basis. Some comparative data were also obtained for the ghost crabOcypode. Animals in the laboratory were maintained on a daily light (L)-dark (D)cycle 12L∶12D. Periods of adaptation ranged from 3–28 h (Table 1) and light adaptation was effected at one moderate intensity equal to the light period in the daily sequence. 2. Massive rapid reversible changes in rhabdom size (Fig. 1) comprising mainly diameter modulation (Figs. 2, 3) and some alteration in length, normally resulted in maximum increases in receptor organelle volume of about 20× between a thinner, shorter fully light adapted condition (2×290 μm) to the fully dark adapted state (7.9× 336 μm). 3. Rhabdom growth during dark adaptation (Table 2) was due mainly (Fig. 8) to microvillus elongation (+154%) as well as substantial increase (+117%) in the number of microvilli present in cross sections (Figs. 2, 3, 10); microvillus diameter (Figs. 4, 5, 9) also increased (+14%) but accounts for only a minor part of the overall change commensurate with observed differences in rhabdom length (+16%). Calculation shows that from fully light adapted to fully dark adapted state the area of photoreceptor membrane increased nearly 20× in a few hours. 4. Although duration of adaptation affected its amplitude, six hours of either light or darkness evoked the maximum changes documented; shorter and longer periods had less effect (Figs. 6, 7). 5. Time of day had a strong periodic influence on the amplitude of membrane adaptation produced by a given exposure to dark or light. Thus maximum dark adaptation occurred with 6 h of darkness terminating at midnight and maximum light adaptation with 6 h of light ending at noon of the diurnal light cycle (Fig. 11). 6. Direct effects of light and dark on synthesis and degradation of photoreceptor membrane must therefore be superimposed on indirect or direct cyclic neuroendocrine control presumably coupled to an entrained circadian oscillator.