The eye of Dytiscus (Coleoptera)

The eye of Dytiscus (Coleoptera) has rhabdomeres at three different levels. The crystalline threads stretch from the ends of the crystalline cones only as far as the distal layer of rhabdomeres. There is one distal rhabdo-mere per ommatidium, and in this system the ommatidia are anatomically separate. Between the distal rhabdomere and the rhabdomeres of the next six retinula cells is a wide clear zone in which light entering by one facet could possibly reach deep rhabdomeres of a different ommatidium. Of the six proximal rhabdomeres, four have rhabdomere tubules which lie horizontal with reference to the normal posture, the other two having vertically oriented tubules. The eighth cell, with nucleus near the basement membrane, has a small rhabdomere. All eight retinula cells have axons and there is no other class of axons in the eye.     

The compound eye of Parnara guttata (Insecta,Lepidoptera, Hesperiidae): Fine structure of the ommatidium

Summary The fine structure of an ommatidium of a skipper butterfly, Parnara guttata, has been studied using the electron microscope. Each ommatidium has nine retinula cells, which were classified into three groups: two distal, six medial and one basal retinula cells. The rhabdomeres of the distal retinula cells are localized in the distal part of the rhabdom, while those of the six medial retinula cells appear throughout most of the rhabdom. The rhabdomere of the basal retinula cell occupies only the basal part of the rhabdom. The rhabdomeres of four medial cells are constructed of parallel microvilli, while fan-like microvilli form the rhabdomeres of other two medial retinula cells. The distal and basal retinula cells have rhabdomeres consisting of both parallel and fan-like microvilli. This is the first time the construction of the rhabdomeres of the distal and basal retinula cells has been described in such fine detail for a skipper butterfly. Nine retinula cell axons of each ommatidium extend to the first neuropile of the optic lobe, the lamina ganglionaris. No difference was found in the number of retinula cells of an ommatidium or the shape of the rhabdom between the dorsal and ventral regions of the compound eye.     

The ultrastructural organization of the visual system of the wax moth,Galleria mellonella: The retina

Summary The ultrastructural organization of ommatidial components of the retina of the moth, Galleria mellonella are described from electron microscopic observations. Each ommatidium is composed of 12 common retinula cells and one basal eccentric cell. The retinula cells are connected together by a desmosomal strip along their length. The rhabdom occupies the basal thirty percent of the ommatidium and can be divided into nine segments of parallel microvilli. Several cells may contribute to an individual rhabdomere. The rhabdomeres are arranged in a cross with single cell rhabdomeres lying between the arms of the cross. Thin sections of ommatidium absorb polarized light differentially. The total amount of plane polarized light absorbed varies with angle of rotation for an entire ommatidium but there are also differences between the amount of absorption of adjacent rhabdomeric segments. Galleria appears to be the only lepidopteran in which the possibility of the polarized light reception has been reported.     

The fine structure of the retina of the honey bee drone

Summary The eye of the honey bee drone is composed of approximately 8,000 photoreceptive units or ommatidia, each topped by a crystalline cone and a corneal facet. An ommatidium contains 9 visual or retinula cells whose processes or axons pierce a basement membrane and enter the optic lobe underlying the sensory retina. The visual cells of the ommatidium are of unequal size: six are large and three, small. In the center of the ommatidium, the visual cells bear a brush of microvilli called rhabdomere. The rhabdome is a closed-type one and formed mainly by the rhabdomeres of the six large retinula cells. The rhabdomeric microvilli probably contain the photopigment (rhodopsin), whose modification by light lead to the receptor potential in the retinula cells. The cytoplasm of the retinula cells contains various organelles including pigment granules (ommochromes), and peculiar structures called the subrhabdomeric cisternae. The cisternae, probably composed of agranular endoplasmic reticulum undergo swelling during dark adaptation and appear in frequent connection with Golgi cisternae. Three types of pigment cells are associated with each ommatidium. The crystalline cone is entirely surrounded by two corneal pigment cells. The ommatidium, including its dioptric apparatus and corneal pigment cells, is surrounded by a sleeve of about 30 elongated cells called the outer pigment cells. These extend from the base of the corneal facet to the basement membrane. Near the basement membrane the center of the ommatidium is occupied by a basal pigment cell. Open extracellular channels are present between pigment cells as well as between retinula cells. Tight junctions within the ommatidium are restricted to the contact points between the rhabdomeric microvilli. These results are discussed in view of their functional implications in the drone vision, as well as in view of the data of comparative morphology.This work was supported by a grant from the Fonds National Suisse de la Recherche Scientifique.     

Fine-structure of the compound eye of the buprestid beetle Curis caloptera (Coleoptera, Buprestidae)

Curis caloptera is a buprestid beetle, which is active in bright sunlight. Its eye, like that of many other diurnal arthropods, is of the apposition type, in which dioptric apparatus and receptor layer are not separated by a region devoid of pigment. Perhaps to prevent damage by U. V.-radiation, the cornea is relatively thick (approximately 90 micron) and crystalline cones are of the "eucone-type". In each ommatidium the cone cell extensions occupy regular positions between the 8 retinula cells and reach down to the basement membrane where they end in bulbous swellings and contain grains of screening pigment. Pigment grains, slightly smaller than those present in the primary pigment cells, are also found within the retinula cells. Although the rhabdom possesses a uniform diameter of approximately 2 micron over its entire length of almost 300 micron, the number of rhabdomeres contributing to the rhabdom varies and depends on the level at which the rhabdom is sectioned. At the distal end, only one retinula cell possesses a rhabdomere; the same holds true for the proximal end, where a different rhabdomere (with microvilli at right angles to those of the distal cell) dominates. One retinula cell, of darker appearance in electron micrographs, occupies a distal position in each ommatidium and remains preferentially oriented within a sector of 60 degrees irrespective of the ommatidial axis. The ommatidial axis itself was found to vary 235 degrees. We provide circumstantial evidence for the view that the cell in question could be a U. V.-receptor with a role to play in an unambiguous determination of the E-vector. Separate bundles, each containing 8 axons, pass through the basement membrane together with 1 or 2 tracheoles. A traceheal tapetum is not developed.     

Electron microscopic studies of the compound eye of the toadbug,Gelastocoris oculatus

There are eight retinula cells in the ommatidium of the compound eye of the toadbug (Gelastocoris oculatus), two of which are central in position. Along the axial sides of the six peripheral retinula cells expand six cytoplasmic processes from the apical crystalline cone cells. These processes, which contain longitudinally-oriented microtubules, are associated with all eight retinula cells by means of desmosomal junctions. In addition to providing structural support, the possibility is set forth that the interconnecting cone processes might also serve to functionally integrate the retinula cells of an ommatidium. The eight retinula cells possess microvillus surfaces, which are especially prominent in the six peripheral cells, where they extend into the lumen of the ommatidium. There is evidence of pinocytotic activity at the bases of microvilli. Multivesicular bodies are present in the cytoplasm of retinula cells, and the means by which these bodies might be elaborated are discussed.     

Specialized ommatidia for polarization vision in the compound eye of cockchafers,Melolontha melolontha (Coleoptera,Scarabaeidae)

Summary The superposition eye of the cockchafer, Melolontha melolontha, exhibits the typical features of many nocturnal and crepuscular scarabaeid beetles: the dioptric apparatus of each ommatidium consists of a thick corneal lens with a strong inner convexity attached to a crystalline cone, that is surrounded by two primary and 9–11 secondary pigment cells. The clear zone contains the unpigmented extensions of the secondary pigment cells, which surround the cell bodies of seven retinula (receptor) cells per ommatidium and a retinular tract formed by them. The seven-lobed fused rhabdoms are composed by the rhabdomeres of the receptor cells 1–7. The rhabdoms are optically separated from each other by a tracheal sheath around the retinulae. The orientation of the microvilli diverges in a fan-like fashion within each rhabdomere. The proximally situated retinula cell 8 does not form a rhabdomere. This standard form of ommatidium stands in contrast to another type of ommatidium found in the dorsal rim area of the eye. The dorsal rim ommatidia are characterized by the following anatomical specializations: (1) The corneal lenses are not clear but contain light-scattering, bubble-like inclusions. (2) The rhabdom length is increased approximately by a factor of two. (3) The rhabdoms have unlobed shapes. (4) Within each rhabdomere the microvilli are parallel to each other. The microvilli of receptor 1 are oriented 90° to those of receptors 2–7. (5) The tracheal sheaths around the retinulae are missing. These findings indicate that the photoreceptors of the dorsal rim area are strongly polarization sensitive and have large visual fields. In the dorsal rim ommatidia of other insects, functionally similar anatomical specializations have been found. In these species, the dorsal rim area of the eye was demonstrated to be the eye region that is responsible for the detection of polarized light. We suggest that the dorsal rim area of the cockchafer eye subserves the same function and that the beetles use the polarization pattern of the sky for orientation during their migrations.     

Twisted rhabdomeres in the compound eye of a tipulid fly (Diptera)

Summary The individual rhabdomeres of the outer retinular cells (R1–6) in the tipulid fly, Ptilogyna, twist about their long axes. Proximally, the rhabdoms become partitioned off by processes from the retinular cells, so that the basal region of each rhabdomere is enclosed in a pocket formed by its own cell (Fig. 2). This organisation of the rhabdom enables each rhabdomere to twist while supported within its own retinular cell, and while the cell itself maintains its orientation with respect to the entire ommatidium. Theory predicts that the rhabdomeral twisting should significantly reduce the polarisation sensitivity of R1–6, but have little effect on the efficiency with which unpolarised light is absorbed.     

Photoreceptor structures. III. Drosophila melanogaster

The eyes of three eye mutants of Drosophila melanogaster were fixed and thin sections studied for its structural detail in the electron microscope. Each ommatidium was found to have seven retinula cells with an equal number of rhabdomeres (visual units). The rhabdomeres average 1.2 micro in diameter and 60 micro in length. Each rhabdomere consists of osmium-fixed dense bands averaging 120 A in thickness, and with less dense interspaces 200 to 400 A. There is an average of 23 dense bands or 46 interfaces per micron within the rhabdomere. The rhabdomere as we have presented it is a single structure of packed rods or tubes. The "fine structure" within the rhabdomere is similar to that observed by electron microscopy for the retinula of the house fly, and to the retinal rods of the vertebrate eye, and to the chloroplasts of plant cells in a variety of animal and plant photoreceptor structures. In addition, the radial arrangements within the ommatidium of radially unsymmetrical units, the rhabdomeres, is probably related to the analysis of polarized light in the insect eye.     

PHOTORECEPTOR STRUCTURES : III. DROSOPHILA MELANOGASTER

The eyes of three eye mutants of Drosophila melanogaster were fixed and thin sections studied for its structural detail in the electron microscope. Each ommatidium was found to have seven retinula cells with an equal number of rhabdomeres (visual units). The rhabdomeres average 1.2 µ in diameter and 60 µ in length. Each rhabdomere consists of osmium-fixed dense bands averaging 120 A in thickness, and with less dense interspaces 200 to 400 A. There is an average of 23 dense bands or 46 interfaces per micron within the rhabdomere. The rhabdomere as we have presented it is a single structure of packed rods or tubes. The "fine structure" within the rhabdomere is similar to that observed by electron microscopy for the retinula of the house fly, and to the retinal rods of the vertebrate eye, and to the chloroplasts of plant cells in a variety of animal and plant photoreceptor structures. In addition, the radial arrangements within the ommatidium of radially unsymmetrical units, the rhabdomeres, is probably related to the analysis of polarized light in the insect eye.     

The fine structure of the compound eye of a damsel-fly

Summary The compound eyes of two species of damsel-flies, Ishunura senegalensis and Cersion calamorum, were examined by electron microscopy. Each ommatidium is composed of eight retinula cells which are semistratified in the receptor layer. The retinula cells are divided into four types from the difference of levels in the rhabdom formation; one distal large cell having the rhabdomere only in the distal layer, four middle cells forming the rhabdom in the middle layer, two proximal cells making up the rhabdom in the proximal layer and one distal small cell having no rhabdomere in any layers. In addition, the lamina ganglionaris was partly observed. Some retinula axons terminate at an different level from the other axons. The functional differentiation among these different types of cells is discussed with relation to the analysis of the polarized light and the discrimination of the diffraction images.This work is supported by a grant from the U.S. Army Research and Development Group (Far East), Department of the Army (DA-CRD-AG-S29-544-67-G61).The authors wish to express their gratitude to Drs. H. Morita and H. Tateda for their helpful discussions throughout this study.     

粘虫蛾复眼背、腹区视杆结构的差异

根据光学和电子显微镜的观察,粘虫蛾复眼背、腹区域的视杆结构具有以下主要差异:1)背方小眼视杆的长度短于腹方小眼视杆的长度。2)在横切面上,背方小眼视杆的中段近似方形。该段间细胞的视小杆为三角形,每个具有平行排列的微绒毛。整个视杆包含两个互相垂直的微绒毛轴。腹方小眼视杆的中段为风扇形。间细胞的视小杆为“V”字形,微绒毛排列不平行。3)背方小眼基细胞的视小杆几乎位于气管反光层远侧,而腹方小眼甚至延伸到气管反光层内。 在背方和腹方小眼视杆的内段,每个间细胞的微绒毛均平行,且排列在基细胞的大形视小杆周围。更深层,在其它细胞的轴突均已相继出现的水平上,基细胞的大形视小杆仍然可见。 最后,对形态上的特点,在功能上可能具有的一些意义也进行了初步讨论。     

Ultrastructure of the compound eye of the diploid female beetle,Xyleborus ferrugineus

Summary The compound eye of female (diploid) Xyleborus ferrugineus beetles was examined with scanning and transmission electron microscopy. The eye is emarginate, and externally consists of roughly 70–100 facets. Each ommatidium is composed of a thickly biconvex lenslet with about 50 electron dense and rare layers. The lens facet overlies a crystalline cone of the acone type which is roughly hourglass-shaped. Pigment cells envelop the entire ommatidium, and pigment granules also are abundant throughout the cytoplasm of the 8 retinular cells. The rhabdomeres of 2 centrally situated photoreceptor cells effectively fuse into a rhabdom that extends from the base of the crystalline cone deeply into the ommatidium. Six distal peripheral retinular cells encircle the 2 central cells, and their rhabdomeres join laterally to form a rhabdomeric ring around the central rhabdom. The rhabdom and rhabdomeric ring are effectively separated by the cytoplasm of the two central retinular cells which contains the usual organelles and an abundance of shielding pigment granules. Eight axons per ommatidium gather in a tracheae-less fascicle before exiting the eye through the fenestrate basement membrane. No tracheation was observed among the retinular cells. Each Semper cell of each observed crystalline cone contained an abundance of virus-like particles near the cell nucleus. The insect is laboratory reared, and the visual system seems very amenable to photoreceptor investigations.This research was supported by the Director of the Research Division, C.A.L.S., University of Wisconsin, Madison; and in part by research grant No. RR-00779 from the Division of Research Resources, National Institutes of Health and by funds from the Schoenleber Foundation, Milwaukee, WI to D.M.N.     

Identificaton of UV,green and red receptors,and their projection to lamina in the cabbage butterfly,Pieris rapae

Summary The photoreceptors in the compound eye of a cabbage butterfly, Pieris rapae, were examined by conventional and intracellular-labeling electron microscopy by the use of the cobalt(III)-lysine complex as an ionized marker. Five types of spectral sensitivity were recorded intracellularly in electrophysiological experiments. They peaked at about 340, 380, 480, 560 and 620 nm, respectively. One of the distal retinula cells (R2) was a UV receptor, whereas the R4 distal retinula cell was a green receptor. The basal retinula cell, R9, was found to be a red receptor; it was localized near the basement membrane, having a bilobed cell body with an individual nucleus in each lobe. A small number of rhabdomere microvilli were present in a narrow cytoplasmic bridge connecting the two lobes. The axons of six retinula cells (R3–R8) in each ommatidium terminated at the cartridge in the lamina (short visual fiber), whereas those of the other three retinula cells, R1, R2 and R9, extended to the medulla (long visual fiber). The information from the UV and red receptors is therefore probably delivered directly to the medulla neurons, independent of that from the other spectral receptor types.     

栖境不同的两种跳甲复眼结构比较

栖息于荫暗隐蔽处的蛇莓跳甲(Altica fragariae)和向阳开阔地的萎陵跳甲(A.Ampelophaga)的复眼外部形态及小眼微细结构有如下相同特征：两复眼均比较小,呈“八”字型排列在头部近背方的两侧;每个小眼含有一个双凸面的角膜锥体、4个森氏细胞和7个小网膜细胞;2个主色素细胞及11-12个附色素细胞围绕在小眼的外缘;小网膜细胞和色素细胞内均有丰富色素颗粒,当光照强度发生变化时,小网膜细胞内的色素颗粒发生位移;在视杆中段横切面上,视杆由7个微绒毛呈平行排列的矩形视小杆组成,其中的6个视小杆互相连成一个近似六边形的框架,将另一个视小杆围在中央。两种跳甲复眼结构的主要差异有：蛇莓跳甲每个复眼大约仅有150个小眼,而萎陵跳甲约有2印个;复眼曲率半径前者只有后者的一半;视杆中段横切面上,视杆占整个小网膜面积的比率两虫分别为37%和25%,蛇莓跳甲高于萎陵跳甲。对以上形态结构特征可能具有的功能意义进行了初步讨论。     

扁豆成熟胚囊的超微结构

本文对扁豆（Dolichos lablab)成熟胚囊的超微结构进行了研究,在成熟胚囊中,卵细胞和助细胞仅在珠孔端1／3有细胞壁,靠近合点端,卵细胞一助细胞,卵细胞－中央细胞,助细胞－中央细胞之间没有细胞壁存在,相邻细胞的质膜靠在一起,在卵细胞和中央细胞的质膜间,有些地方存在中等电子密度的物质,卵细胞的细胞质中含有很多的线粒体和质体,内质网和高尔基体较少,助细胞的珠孔端有一复杂的丝状器,靠近珠孔端的细胞质中有很多管状的内质网,表明助细胞可能具有分泌功能,在助细胞的合点端,含有丰富的粗糙内质网,助细胞和卵细胞的质膜之间有很多囊泡状的结构,中央细胞内含有丰富的线粒体,高尔基体和内质网,中央细胞的壁向内形成突起,在周缘细胞质中含有丰富的脂滴。     

The micromorphology of the nauplius eye of the estuarine calanoid copepod, Sulcanus conflictus Nicholls (Crustacea)

The nauplius eye consists of one median and two lateral ocelli, each within a pigment cup. The three pigment cups are made up from two multi-nucleate pigment cells: each cell forming one lateral cup and half of the median cup. The three cups are lined on the insides by tapetal cells which contain layers of reflectile crystals. Each of the ocelli contains six sensory cells which protrude from the rims of the pigment cups and the protruding parts are sheathed by the conjunctiva cells. The whole eye is enveloped by a thin membrane which also sheaths the proximal parts of the five nerve bundles that leave the eye. All the sensory cells of the lateral ocelli are similar and have rhabdomeric microvilli on the terminal end, and contain phaosomes and a multitude of other organelles and cytoplasmic inclusions. The complex median ocellus contains a superior group of three retinular cells, linked by interdigitating processes, and an inferior group consisting of a large central cell enclosed in two cup-shaped peripheral retinular cells. A two-tiered rhabdome arrangement exists, with a rather complex inferior rhabdome set made up of a central rhabdomere and two hemi-annulate rhabdomeres. The cytoplasm of the retinular cells of the median ocellus lack phaosomes but instead contain double-walled tubular elements, possibly formed by the inpushings of microvilli into adjacent cells. The possible functional significance of the unique arrangement seen in the median ocellus is discussed. The retinular cells are of the inverse type. There are no efferent nerve fibres from the brain nor any nervous connection between the lateral and the median ocelli.     

The distal ommatidium of the compound eye of the housefly (Musca domestica): A scanning electron microscope study

The distal aspect of the housefly ommatidium was surveyed by the scanning electron microscope. Attention was directed to the somal eminence of the superior central cell and the lens to large pigment cell junction. The underside of each lens facet exhibits six hexagonally arranged incisures. Into each of these indentations are fitted several large pigment cells. This hexagonal indentation appears to be a tenacious anchorage. Two corneal pigment cells laterally encircle the pseudocone and at their proximal extension they enclose the Semper cells and neck of the retinula. The somal eminence of the superior central cell is about 10 mum from the base of the corneal pigment cell enclosure. Micrographs were used to construct a diagram of the ommatidium above the basement membrane. Suggestions are made as to the functional correlates of the observed ommatidial structures.     

The ultrastructure of the cornea-lens epidermis in the lateral eye of Limulus polyphemus

The structure of the “Corneagen,” i.e., the epidermis lying beneath the cornea-lens of the lateral eyes of the adult intermolt Limulus polyphemus was studied with light and electron microscopy. This layer is composed of heavily columnar cells containing a striking number of cytoplasmic microtubules. Many of the microtubules are grouped into compact bundles or fascicles, generally each cell having at least one microtubule bundle. The cornealens end of each cell has numerous microvilli, each with a core of delicate filaments. The crypts between microvilli end in extracellular expansions and plaques of electron dense amorphous material are associated with these terminal expansions. Cytoplasmic microtubules appear to insert into these dense areas. The basal ends of the cells are thrown into many pseudopodial processes which extend into the surrounding extracellular space. The cytoplasm of the pseudopodia is composed largely of microtubules and their associated low density halos. Junctional complexes consisting of zonulae adhaerens and septate desmosomes are present between adjacent cells. Mitochondria, ER, cytoplasmic vesicles, Golgi stacks and other ultrastructural details of the epidermal cells are described. The ultrastructure of a column of pigment free processes lying between the apex of the lens cone and the underlying photoreceptive portion of the ommatidium is also described. Ducts or vessels of uncertain origin are present in the inter-ommatidial spaces. Possible roles played by the microtubules, the significance of their disposition and of their association with the dense subsurface plaques are discussed in terms of intracellular support, epidermis-lens attachment and extracellular pattern determination. In addition, the likelihood of the dense plaques being the site of microtubule assembly is considered.     

柚木野螟成虫复眼外部形态和超微结构观察

【目的】柚木野螟Eutectona machaeralis主要取食危害珍贵树种柚木。本研究旨在观察研究柚木野螟成虫复眼的形态、组织结构和超微结构,分析其复眼结构特征,为更好了解该物种复杂的视觉行为与感光、趋光机制的关系奠定基础。【方法】运用光学显微镜以及扫描和透射电子显微镜技术观察了柚木野螟成虫复眼的形态、组织结构和超微结构。【结果】柚木野螟成虫复眼着生于头部触角基部,呈椭球形,属对称性复眼。雌、雄成虫复眼分别有2 300~2 755和1 950~2 316个小眼。小眼呈正六边形,表面密被角膜乳突,间隙偶有感觉毛。每个小眼由1个角膜、4个晶锥细胞、1对初级色素细胞,6个次级色素细胞、不同水平面分布的12个视网膜细胞和基膜等组成。沿小眼纵轴11个视网膜细胞的向心侧细胞膜特化成细丝状微绒毛,形成放射状排列的视小杆,组合呈融合型视杆;第12个视网膜细胞位于小眼基部。基膜上方,视网膜细胞和次级色素细胞末端膨大,以轴突形式穿过基底膜。【结论】柚木野螟复眼为典型的重叠像眼,雌、雄成虫小眼排列方式及内部结构无明显差异,但雌、雄虫小眼数量和大小具有明显的性二型现象。