scholarly journals Profile of a decaying crystalline cone

1999 ◽  
Vol 60 (8) ◽  
pp. 5946-5962 ◽  
Author(s):  
Navot Israeli ◽  
Daniel Kandel
Keyword(s):  
Crystalline Cone

Eye structure and optics in the pelagic shrimp Acetes sibogae (Decapoda, Natantia, Sergestidae) in relation to light-dark adaptation and natural history

1986 ◽  
Vol 313 (1160) ◽  
pp. 251-270 ◽  
Keyword(s):  
Natural History ◽  
Basement Membrane ◽  
Focal Length ◽  
Pigment Cells ◽  
Retinula Cell ◽  
Maximum Diameter ◽  
Membrane Turnover ◽  
Image Brightness ◽  
Crystalline Cone ◽  
Cone Cells

The structure and optics of the compound eyes of the neritic sergestid shrimp, Acetes sibogae , are described. The eyes are nearly spherical and heavily pigmented. The facets are square, indicating that the eye operates by the recently recognized mechanism of reflecting superposition. The most distal portion of each ommatidium is the corneal lens, which is secreted by two underlying corneagenous cells. These two cells surround the crystalline cone and cone stalk and the four cells of which they are composed and extend proximally at least as far as the distal rhabdom. Near the base of the cone stalk the extensions of the corneagenous cells swell and enclose spheres which bear on their surfaces small particles similar to ribosomes in appearance. Beneath the corneagenous cells lie four crystalline cone cells, parts of which differentiate to form the crystalline cone and cone stalk. The latter structures are compound, one quarter of each being contributed by each crystalline cone cell. Distally the crystalline cone cells send a small projection, which is surrounded by the corneagenous cells, to the cornea. Proximal extensions of each of the four parts of the cone stalk extend between the retinula cells and meet within the basement membrane. Between the base of the cone stalk and the regularly layered rhabdom lies the distal rhabdom. It is surrounded by a cell that we have termed retinula cell eight (R8), by analogy with other crustacean systems, and consists of unordered microvilli projecting from the cell membrane into the extracellular space above the layered rhabdom. In addition to R 8, which contributes only to the distal rhabdom, seven other retinula cells contribute to the proximal rhabdom, which consists of alternating ordered layers of orthogonally arranged microvilli. Four of these retinula cells are arranged orthogonally and extend far distally along the crystalline tract. The other three do not extend as far distally and alternate with the first four in their position around the axis of the ommatidium. R8 is located still further proximally at the level of the distal rhabdom. All seven of the retinula cells which contribute to the proximal rhabdom contain proximal pigment and extend through the basement membrane. The basement membrane consists of a meshwork grid with each intersection supporting a rhabdom so at this point the retinula cell axons project into different squares of the meshwork. Tapetal pigment cells are present in the vicinity of the basement membrane and extend downward to the lamina. The granules of tapetal pigment are covered or exposed by movements of the proximal pigment and also change their intracellular distribution depending on illumination. In addition to the proximal (retinula cell) pigment and the tapetal pigment the eye contains four types of distal pigment. Moving inward from the cornea these are the distal yellow pigment (DYP) which surrounds the entire eye; the distal reflecting pigment (DRP), which forms a thin layer and is continuous with the tapetal pigment at the edge of the eye; and the black distal pigment and the mirror pigment (MP) both contained within distal pigment cells (DPC). In the light-adapted state the proximal pigment moves distally, surrounding the rhabdoms, and the tapetal pigment granules move proximally so that they are mainly found beneath the basement membrane. Movements of the distal pigments are less clearcut, but they all appear to move somewhat proximally in the light-adapted state. Multivesicular bodies are more abundant in the retinula cells shortly after dawn, and are possibly related to membrane turnover. Interommatidial angle, as measured on both fixed and fresh material, varied from 2.8 to 3.8° in different parts of the eye. The crystalline cones were found to have a uniform refractive index radially, which, combined with their square shape, indicates that they function by reflecting superposition. Total internal reflection from the sides of the cones is adequate to explain the maximum diameter of the eyeshine from the dark-adapted eye at night without the need for additional mirrors. Nevertheless, from its organization and appearance the mirror pigment could act as a reflector in the dark-adapted eye. Also, the size of the glow patch indicates that there would be a gain of nearly two log units in image brightness in going from the light-adapted to the dark-adapted state. Each corneal facet was found to act as a weak converging lens, with a focal length of approximately 300 μm. The eye structure of Acetes is discussed in relation to that of other shrimp and to the natural history of Acetes .

The phylogenetic significance of ommatidium structure in the compound eyes of polyphagan beetles

1986 ◽  
Vol 64 (9) ◽  
pp. 1787-1819 ◽  
Author(s):  
Stanley Caveney
Keyword(s):  
Compound Eyes ◽  
Beetle Species ◽  
Phylogenetic Significance ◽  
Lens System ◽  
Crystalline Cone ◽  
Progressive Loss ◽  
Open Rhabdom ◽  
Scarab Beetles

The structure of ommatidia in adults of more than 200 beetle species from 91 polyphagan families was surveyed. Three basic types of lens system (eucone, exocone, and acone) and two types of retinal unit (fused rhabdom, open rhabdom) are represented. The eucone (crystalline cone-containing) ommatidium is ancestral and prevails in primitive Eucinetoidea, Hydrophiloidea, and Scarabaeoidea; ommatidia of the primitive beetles Cupes and Omma as well as the Adephaga are of this type. The polyphagan founders most likely had ommatidia with small crystalline cones and narrow clear zones beneath the corneal facets. Exocone and acone eyes are derived structures, and their distribution suggests that both have evolved several times. Exocone ommatidia arose early in polyphagan evolution, possibly first in dascilloid-like founders of elateriform and bostrychiform beetles, where the exocone is commonly found. An exocone eye also evolved separately in the ancestors of several primitive scarabaeoid families; possible steps in this eucone to exocone transition may be seen in the Trogidae. The clear zones of eucone and exocone eyes are not homologous. The acone ommatidium is specialized and arose through a progressive loss of either crystalline cone or exocone. In the advanced staphylinoid beetles it is a relic of crystalline cone loss in their small ancestors. In the cucujiforms it arose likely from the loss of the exocone in their bostrychiform ancestors, associated here with a shift to an open rhabdom. Although the distribution of ommatidial types coincides with major lineages in the Polyphaga, a few anomalies remain. The Eucnemidae, Buprestidae, and Dryopidae are all eucone yet are placed in the elateriform series, in which 25 of 30 families are exocone. Scarab beetles have an extraordinary variety of lens types that presumably reflects the exceptional adaptability of the eye in this superfamily.

Memoirs: The Eye and Optic Tract of Insects

1885 ◽  
Vol s2-25 (98) ◽  
pp. 215-251
Author(s):  
SYDNEY J. HICKSON
Keyword(s):  
Comparative Anatomy ◽  
Optic Tract ◽  
Intermediate Stage ◽  
Crystalline Cone ◽  
Similar Series ◽  
First Time

In this memoir, then, I have described in detail the eye and optic tract of Muse a vo mitoria. The pseudo-cones I have found to be composed of four cells with their nuclei situated internally, each one containing a large watery or albuminous vacuole, which serves the same purpose, and is morphologically homologous with the crystalline cone of the "eucone" eyes. There are six retinulte cells, each possessing a nucleus situated in that part of it which lies immediately behind the pseudocones, and in some cases an additional nucleus, situated about half way down. I have figured for the first time the interommatidiai tracheal vesicles which have been previously observed by several investigators. In the optic tract I have described three ganglia--the opticon, epi-opticon, and periopticon. The last of these is composed of a number of small cylindrical elements of a tissue composed of a sponge work of nerve-fibrilæ, which I have called a "neurospongium." The opticon and the epi-opticon are present in all insects and in most of the higher Crustacea. The peri-opticon appears comparatively late in development, but is never found even in the adults of Periplaneta and Nepa. The peri-opticon, when present, is usually composed of a number of cylindrical elements, which partially fuse in Aeschna and completely in Eristalis, Bombyx, and the Crustacea. In Eristalis the peri-opticon is traversed by a number of delicate tracheal vessels. The terminal optic anastomosis of Nepa is more complicated than it is in Periplaneta, and seems to be an intermediate stage between the simple anastomosis and the true peri-opticon of Musca. A similar series of intermediate stages between the simple anastomosis and a true peri-opticon has been traced in the development of these parts in the Bee. The development and comparative anatomy of the periopticon of insects is interesting, as it may indicate the mode in which central ganglia were first formed from primitive nerve-fibrils and cells. My researches seem to me to corroborate the opinion of the majority of previous investigators, that the retinulas are the true nerve-end cells. My researches were carried on entirely in the morphological laboratory at Oxford, and I have to thank Professor Moseley for much valuable help and advice, and to Professor Lankester for many valuable suggestions.

scholarly journals Some aspects of vision in the lobster, Homarus vulgaris, in relation to the structure of its eye

1963 ◽  
Vol 43 (3) ◽  
pp. 683-699 ◽  
Author(s):  
Elizabeth M. Kampa ◽  
Bernard C. Abbott ◽  
Brian P. Boden
Keyword(s):  
Compound Eye ◽  
Crystalline Cone ◽  
Cone Cells ◽  
Retinular Cells

The compound eye of the lobster H. vulgaris has a single lobe; its ommatidia are uniform except in length. Each ommatidium consists of a corneal facet, two corneagenous cells, four cone cells, a four-part crystalline cone, an elongate cone stalk, seven retinular cells and a four-part rhabdom. Growth between the zoaeal and adult stages is primarily a lengthening of the cone stalk.

The compound eye as an indicator of age and shrinkage in Antarctic krill

1995 ◽  
Vol 7 (4) ◽  
pp. 387-392 ◽  
Author(s):  
S. Sun ◽  
William De La Mare ◽  
Stephen Nicol
Keyword(s):  
Body Length ◽  
Antarctic Krill ◽  
Compound Eye ◽  
Natural Populations ◽  
Late Summer ◽  
Euphausia Superba ◽  
The Body ◽  
Laboratory Population ◽  
Number Count ◽  
Crystalline Cone

Laboratory studies have shown that Antarctic krill (Euphausia superba) shrink if maintained in conditions of low food availability. Recent studies have also demonstrated that E. superba individuals may be shrinking in the field during winter. If krill shrink during the winter, conclusions reached by length-frequency analysis may be unreliable because smaller animals may not necessarily be younger animals. In this study, the correlation between the body-length and the crystalline cone number of the compound eye was examined. Samples collected in the late summer show an apparent linear relationship between crystalline cone number and body-length. From a laboratory population, it appears that when krill shrink the crystalline cone number remains relatively unchanged. If crystalline cone number is little affected by shrinking, then the crystalline cone number may be a more reliable indicator of age than body-length alone. The ratio of crystalline cone number to body-length offers a method for detecting the effect of shrinking in natural populations of krill. On the basis of the crystalline cone number count, it appears from a field collection in early spring that E. superba do shrink during winter.

Daily changes in the compound eye of a beetle ( Macrogyrus )

1983 ◽  
Vol 217 (1208) ◽  
pp. 265-285 ◽  
Keyword(s):  
Point Source ◽  
Light Adaptation ◽  
Compound Eye ◽  
Lucifer Yellow ◽  
Dense Layer ◽  
Clear Zone ◽  
Acceptance Angle ◽  
Crystalline Cone ◽  
Graded Index ◽  
Peak Sensitivity

(i) Graded index lenses in the cornea and the crystalline cone form the optical system in each ommatidium. (ii) By night the crystalline cone has a blunt ellipsoidal proximal end which contributes to the formation of a superposition image across the clear zone. By day the cone is a tapering point that is extended as a light guide through a dense layer of pigment. (iii) The action of extending the cone and moving the pigment towards the clear zone from between the cones occurs as the retinula-cell column contracts. (iv) Modelling of the ommatidial lens system shows how the superposition image is formed in the night eye, and suggests that axial rays are not well focused on the crystalline tract in the day eye. (v) All cells had peak sensitivity in the green near 552 nm. (vi) In the dark-adapted day eye, fields are ∆ ρ (acceptance angle) = 3.4–6.6°, narrowing to 2.8° minimum upon light adaptation. Sensitivity to a point source on axis is reduced during the day: the dark-adapted day eye requires 200 times more light to give the same response as the dark-adapted night eye. There is a further attenuation of about 100 upon light adaptation of the day eye. (vii) The superposition image of the night eye produces fields of width ∆ ρ = 12-15° at 50% sensitivity as recorded electrophysiologically, and therefore the image of a point source covers several rhabdoms. (viii) In recordings from single units in the night eye two bumps (effective photon captures) are counted when the intensity is such that one photon falls on the area of one facet, with parallel axial illumination at the peak of the spectral sensitivity, 552 nm. (ix) Marking of cells with Lucifer Yellow suggests that about four to six receptor units per ommatidium are involved, giving a sensitivity of eight to twelve bumps for the ommatidium at this intensity. (x) Locust apposition eyes, with facets twice the area of those in Macrogyrus eyes, give at best 0.5 bumps with the same intensity, so that the actual superposition gain is 32–48. (xi) All marked cells were of the proximal rhabdom layer; cells 1 and 8 have not been investigated.

Design of graded-index lenses in the superposition eyes of scarab beetles

1981 ◽  
Vol 294 (1075) ◽  
pp. 589-632 ◽  
Keyword(s):  
Refractive Index ◽  
Focal Plane ◽  
Focal Point ◽  
Image Plane ◽  
Optic Axis ◽  
Clear Zone ◽  
Crystalline Cone ◽  
Screening Pigment ◽  
Corneal Lens ◽  
Intermediate Image

Superposition-image quality in the clear-zone eye depends in the first instance on the optical characteristics of the lens elements in each ommatidium. The optical design strategy of the two lens elements, a thick corneal facet and an underlying crystalline cone, in the scarab eye is reported. The formation of a good superposition image at the rhabdom layer in the eye demands that the lens elements be precisely arrayed, virtually free of optical aberrations, and that each lens pair function as an afocal (telescopic) lens system with an internal intermediate focal plane. The optical properties of the corneal facet were examined by a variety of means. The isolated corneas of most scarab species focused good quality images of a distant object. Cardinal-point analysis of the intact corneal lens revealed that the back focal point of the lens lies just proximal to the inner corneal surface, many micrometres distal to the rhabdom layer, and the position of the principal planes suggested that the corneal lens had internal lens-cylinder properties. This was confirmed by the examination of the focusing power of transverse lens slices of known thickness; the power of the corneal lens slice was a function of its thickness. Interference refractometry of corneal sections revealed that the facet is a graded-refractive-index (g.r.i.) lens in the great majority of more than 40 scarab species examined. The position of the back focal point is achieved in a thick corneal lens by (i) the presence of a g.r.i. lens, best developed in the proximal corneal region, where it consists of a g.r.i. lens cylinder capped by a g.r.i. lens hemisphere, and (ii) the loss of front facet curvature in the homogeneous distal corneal region. In situ , the back focal point lies deep within the crystalline cone. Since the quality of the superposition image depends on the exact location of the intermediate-image plane in the crystalline cone, this position was determined from a comparative analysis of cone shape, experimental observations, and theoretical modelling of the cone. Four observations, namely the presence of a waist in the crystalline cone of many species, the back focal distance of the isolated cornea when the refractive index (r.i.) of the medium in the back focal space approximated that situ, the presence of screening pigment around specific regions of the crystalline cone and the position of the intermediate-image plane in the exocone of a passalid beetle eye, all suggested that the intermediate focus lies in the waist region. The proximal region of the crystalline cone was modelled on the basis of its known g.r.i. lens properties. The model used comprised a radial g.r.i. lens cylinder with a parabolic profile in r.i., terminating in a g.r.i. lens hemiellipsoid. Dimensions and r.i. distribution in the model were based on values from real cones. The model cone focused an incident parallel beam to a point within the cone corresponding to the waist region in real cones. For beams at angles as great as 20° to the optic axis, aberrations in the model cone are small, and restricted to the most peripheral rays. A homogeneous hemiellipse of similar dimensions has severe aberrations for beams at an angle to the optic axis. The model predicts that the ommatidial optics are diffraction-limited; the spread of rays leaving the proximal cone tip due to diffraction at the small exit aperture of the cone (for all aperture diameters) is broader than that due to lens aberrations. Consequently, tolerance exists to optical imperfections in the lens components and their spacing. A tolerance in the position of the intermediate focal plane of + 2-3 pm was calculated. Lens design is strongly correlated with the daily activity pattern of the scarab species under consideration. The corneal facets of nocturnal and crepuscular species are wide with little individual facet curvature; such ‘glacial’ corneas are completely transparent. The crystalline cone is large and well developed. In diurnal species, the corneal facets are narrower, with strong individual curvature, and the corneal lens cylinders are often lined with a brown screening pigment. The crystalline cones of diurnal scarabs are frequently strongly waisted or greatly reduced in size. Pigment surrounding the cone waist serves as a field stop limiting the angular acceptance of the ommatidial optics. The waist limits the number of ommatidia that can contribute to the superposition image and therefore determines the maximum aperture of the eye. This aperture is greatest in nocturnal species with little or no waist constriction in the crystalline cone. Most scarab clear-zone eyes are of the eucone type (separate crystalline cone). However, in the Passalidae and bolboceratine and pleocomine Geotrupidae, the crystalline cone is replaced by a corneal g.r.i. lens extension, the exocone, that serves as an optical analogue of the crystalline cone.

Graded-index optics are matched to optical geometry in the superposition eyes of scarab beetles

1985 ◽  
Vol 311 (1149) ◽  
pp. 237-269 ◽  
Keyword(s):  
Refractive Index ◽  
Optical Properties ◽  
Significant Proportion ◽  
Spatial Relationship ◽  
Front Surface ◽  
Three Dimensions ◽  
Lower Sensitivity ◽  
Image Brightness ◽  
Optical Geometry ◽  
Crystalline Cone

Detailed measurements were made of the gradients of refractive index (g.r.i.) and relevant optical properties of the lens components in the ventral superposition eyes of three crepuscular species of the dung-beetle genus Onitis (Scarabaeinae). Each ommatidial lens has two components, a corneal facet and a crystalline cone; in both of these, the gradients provide a significant proportion of the refractive power. The spatial relationship between the lenses and the retina (optical geometry) was also determined. A computer ray-trace model based on these data was used to analyse the optical properties of the lenses and of the eye as a whole. Ray traces were done in two and three dimensions. The ommatidial lenses in all three species are afocal g.r.i. telescopes of low angular magnification. Parallel incident rays emerge approximately parallel for all angles of incidence up to the maximum. The superposition image of a distant point source is a small patch of light about the size of a rhabdom. There are obvious differences in the lens properties of the three species, most significantly in the shape of the refractive-index gradients in the crystalline cone, in the extent of the g.r.i. region in the two lens components and in the front-surface curvature of the corneal facet lens. These give rise to different angular magnifications M of the ommatidial lenses, the values for the three species being 1.7, 1.3, 1.0. This variation in M is matched by a variation in optical geometry, most evident in the different clear-zone widths. As a result, the level of the best superposition image lies close to the retina in the model eyes of all three species. The angular magnification also sets the maximum aperture or pupil of the eye and hence the brightness of the image on the retina. The smaller M , the larger the aperture and the brighter the image. By adopting a suitable value for M and the appropriate eye geometry, an eye can set image brightness and hence sensitivity within a certain range. Differences in the eye design are related to when the beetles fly at dusk. Flight experiments comparing two of the species show that the species with the higher value for M and corresponding lower sensitivity, initiates and terminates its flight earlier in the dusk than the other species with 2.8 times the sensitivity.

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