The fine structure of the ocelli of Triatoma infestans (Hemiptera: Reduviidae)

The morphology and fine structure of the ocelli of Triatoma infestans have been analyzed by means of light and electron microscopy. The two dorsal ocelli of this species are located behind the compound eyes, looking dorsally and frontally. Externally, the ocelli are marked by the corneal lenses virtually spherical in form and limited internally by a cuticular apodeme. The lens focuses the incoming rays beyond the retina. A single layer of corneagen cells lies below the cuticular lens. The corneagen cells and photoreceptors are arranged in a cup-like fashion beneath the cuticular lens. A distal retinal zone comprises the rhabdoms, which are laterally connected in an hexagonal meshwork. A middle retinal zone comprises the receptor cell segment free of rhabdom, and a proximal zone their axons. In the middle zone, the oviform nuclei and spheroids are located. Screening pigment granules are present within the retinal cell. Spherical mitochondria are homogeneously distributed in the cytoplasm of the cell body. In the axonal zone, mitochondria are found in the peripheral region. Axons from receptor cells extend into the ocellar neuropile at the base of the ocelli, to synapse with second order neurons. The large axons of second order neurons are bundled by glial cells. The ocellar plexus exhibits a high diversity of synaptic unions (i.e. axo-dendritic, axo-axonic, dendro-axonic, and dendro-dendritic).     

Ocellar atavism in Coleoptera: plesiomorphy or apomorphy?

Ocelli and ocellus‐like structures on the vertex of the adult head were examined in different representatives of Coleoptera and the presence of these was confirmed for the suborder Polyphaga. The presence of structures, which are likely homologous with ocelli of other insects were confirmed by semi‐thin sectioning in Hydraenidae, Staphylinidae, Derodontidae and Dermestidae. The presence of ocelli is newly recorded for a representative of Scydmaenidae (Nesuthia fijii Franz). The weakly pigmented areas on the vertex of Neopelatops (Leiodidae) lack a lens and associated nervous tissue and are referred to as pseudocelli, which may be present in other groups. The internal structure of Coleopteran ocelli is strongly simplified compared with other groups of Insecta where longitudinal retinula cells are arranged at a right angle to the cuticular surface and enclosed by a sheath of pigment cells. Such a regular arrangement is absent from all beetles examined histologically. A flattened group of cells without a rhabdom and without an enclosing layer of pigment cells is present underneath the cuticular lens. While, the infrastructure of the ocelli is more or less reduced in Coleoptera, the presence of these features in the ground‐plan of Coleoptera is dependent on the confirmation of the presence of ocelli in Archostemata (Jurodidae?) and a robust phylogenetic hypothesis for the order.     

THE MICROSTRUCTURE OF THE COMPOUND EYES OF INSECTS

The apposition eyes of two diurnal insects, Sarcophaga bullata (Diptera) and Anax junius (Odonata), have been examined with the electron microscope. In the latter case only the rhabdom is described. The rhabdom of the fly consists of a central matrix and seven rhabdomeres, one for each retinula cell. The rhabdomeres show an ordered internal structure built up of transverse tubes, hexagonal in cross-section. These slender compartments running the width of the rhabdomere are 370 A in diameter. After fixation with osmium tetroxide the walls of the compartments are more electron dense than the interiors. The retinula cells contain mitochondria, and pigment granules smaller than those found in the pigment cells. These granules tend to cluster close behind the membranes which separate the retinula cells from their rhabdomeres. The rhabdom of the dragonfly is a single structure which appears to be composed of three fused "rhabdomeres," each similar to a rhabdomere of Sarcophaga. Reasons are given for believing that the rhabdom may be the site of photoreception, as well as the organ for analyzing plane-polarized light, as suggested by other workers.     

家蚕复眼突变系光泽眼（lu）和光泽小眼（ve）的复眼形态观察

家蚕Bombyx mori复眼突变系光泽眼(lustrous, lu）及光泽小眼(varnished eye, ve）都是由单基因控制的隐性突变, 目前为止, 其突变基因及突变机理还未知。为了了解其复眼突变性状内外部形态结构差异, 本研究以家蚕正常品系大造Dazao （Dz）为对照, 利用光学显微镜及扫描电镜对家蚕Dz, lu和ve的成虫复眼和幼虫单眼表面进行观察, 并利用石蜡切片HE染色技术对3个品系复眼内部结构进行观察。结果表明： 突变体lu和ve的复眼表面形态除了典型的富有光泽外, 复眼形状、 大小和小眼形态、 排列及数量上都与正常型明显不同。突变体lu和ve的角膜、 晶锥、 感杆束及色素细胞均发生了异常。lu和ve不仅是复眼表面形态发生了变化, 其内部结构也发生了很大的变化。本研究为lu和ve突变基因的克隆及突变机理的阐明提供了参考信息。     

The fine structure of the lateral ocellus of the dobsonfly larva

The lateral ocelli of the dobsonfly (Protohermes grandis, Neuroptera) larva have been examined with light and electron microscopy. The larva has six ocelli on both sides of the head, each containing a single corneal lens. A conical crystalline body, of some 10–20 cells is situated immediately posterior to the lens. From 100 to 300 elongated retinular cells are arranged perpendicular to the crystalline body except at the innermost surface of the lens, where they are absent. The distal process of each retinular cell is enclosed by a tube-like rhabdom formed by the close association of microvilli from the same and adjacent distal processes. The distal process contains many mitochondria, multivesicular bodies, microtubles and pigment granules. In the dark-adapted ocellus the pigment granules are concentrated near the nucleus which lies under the rhabdomic layer. The granules diffuse toward the rhabdomic microvilli during light adaptation. Each retinular cell has a single axon, which extends from the ocellus as an ocellar nerve fiber into the optic lobe, where it frequently synapses upon second order neurons. In addition to these afferent synapses, there are two other synaptic combinations: (1) a feedback synapse from a second order neuron to a retinular axon, and (2) a synapse between second order neurons. These results suggest that photic signals reach the more proximal part of the brain via second order neurons after some degree of integration in the optic lobe.     

The Ultrastructure of the Compound Eye of Two Species of Marine Ostracodes (Crustacea: Ostracoda: Cypridinidae)

Ultrastructurally, the compound eyes of the luminescent marine ostracodes Vargula graminkola and V. tsujii are similar. These ostracodes have two lateral compound eyes, with relatively few ommatidia (13 and 20 respectively). They exhibit apposition type compound eyes as seen in many other arthropods. Each ommatidium includes: a flat, ectodermal cuticular covering, corneagen cells, two long cone cells that give rise to a large conspicuous crystalline cone, retinular cells, pigment cells, a microvillar rhabdom and proximal axonal neurons. The axons merge to form an optic nerve that extends into the brain through a short, muscular stalk that is surrounded externally by a cuticle. The number of retinular cells is typically six per ommatidium in V. graminicola and eight per ommatidium in V. tsujii. Screening pigment cells surround each ommatidium forming a layer that is about 5–15 pigment granules thick. In addition to pigment cells, the cytoplasm of the retinular cells includes numerous screening pigment granules. In light/dark adaptation, there are no obvious morphological differences in the orientation of the rhabdom or in the organization of the screening pigments. Both Vargula species studied are nocturnally active and bioluminescent suggesting that these eyes are capable receptors of the bright conspecific luminescence.     

不同波长光照对三疣梭子蟹复眼超微结构的影响

三疣梭子蟹(Portunus tritubereulatus)经过30 min暗适应后,在不同波长的红光(750 nm),黄光(580 nm),绿光(560 nm),蓝光(400 nm)下,其光感受器形态和超微结构随不同波长光的适应而发生变化。在红光下感杆束直径大,微绒毛排列最整齐,内质网、线粒体等胞器较多,色素颗粒分布均匀,膜下储泡囊小;在蓝光下感杆束直径最小,微绒毛最凌乱,多囊体、板膜体、膜下储泡囊等胞器较多,色素颗粒位于细胞核周围。     

飞蝗复眼生理和结构上的节律变化

采用细胞内记录和光镜方法研究了飞蝗(Locusta migratoria)夜间和日间在暗适应和明适应状态下小网膜细胞角敏感度以及晶锥和小网膜细胞之间区域结构上的变化.结果表明小网膜细胞角敏感度的变化不仅仅由于晶锥周围主色素细胞色素颗粒的移动,而且也由于小眼感杆束结构上的节律变化.     

黑翅土白蚁有翅成虫复眼的形态结构

采用组织切片法光镜下观察黑翅土白蚁Odontotermes formosanus(Shiraki)有翅成虫的复眼形态结构及光、暗适应条件下色素颗粒移动的规律。结果如下:(1)头正前方观,复眼外部形态略呈圆形。(2)有翅成虫复眼类型属于并列像眼,每只复眼约由360个小眼组成。(3)每个小眼是由1套屈光器(1个角膜和1个晶锥)、小网膜色素细胞、视杆和基细胞等几部分组成。小网膜色素细胞内均含有丰富的色素颗粒。(4)在光适应条件状态下,屈光器及视杆周围的色素颗粒主要分布在视杆部位的上侧,暗度适应条件状态时则较均匀地分布于视杆两侧上下;性别对色素颗粒分布无明显影响。     

昆虫单眼的结构和功能

大多数昆虫的视觉器官除了复眼外还有一些简单的小眼,称为单眼。昆虫成虫和半变态类若虫的单眼称为背单眼,位于头顶两复眼之间。背单眼在数目和结构上都有较大变化,但基本结构包括角膜晶体、一层角膜生成细胞(覆盖在角膜晶体上)、视网膜(由大约1000个感光细胞构成,视类群而不同)。背单眼对弱光比较敏感,但在图像感知方面的作用并不显著;它是一种“激发器官”,可以增加复眼的感知能力。全变态昆虫的幼虫既没有复眼也没有背单眼,但在其头部两侧有些类似复眼小眼的侧单眼。侧单眼的结构也与小眼相似,包括角膜,晶体和由一些视网膜细胞组成的视杆。侧单眼是完全变态类昆虫幼虫仅有的感光器官,与复眼一样,它们可以感知颜色、形状、距离等等。     

Redifferentiation of dedifferentiated human chondrocytes in high-density cultures

The ommatidia in the ventral two-thirds of the compound eye of male Pieris rapae crucivora are not uniform. Each ommatidium contains nine photoreceptor cells. Four cells (R1-4) form the distal two-thirds of the rhabdom, four cells (R5-8) approximately occupy the proximal one-third of the rhabdom, and the ninth cell (R9) takes up a minor basal part of the rhabdom. The R5-8 photoreceptor cells contain clusters of reddish pigment adjacent to the rhabdom. From the position of the pigment clusters, three types of ommatidia can be identified: the trapezoidal (type I), square (type II), and rectangular type (type III). Microspectrophotometry with an epi-illumination microscope has revealed that the reflectance spectra of type I and type III ommatidia peak at 635 nm and those of type II ommatidia peak at 675 nm. The bandwith of the reflectance spectra is 40-50 nm. Type II ommatidia strongly fluoresce under ultra-violet and violet epi-illumination. The three types of ommatidia are randomly distributed. The ommatidial heterogeneity is presumably crucial for color discrimination.     

龟纹瓢虫成虫的复眼形态及其显微结构

利用光镜、组织切片法观察了龟纹瓢虫Propylaea japonica(Thunberg)成虫的复眼形态及其显微结构。结果如下:(1)头正前方观,复眼外形似半球,且后方稍向内合拢。每个复眼约包括630个小眼。(2)每个小眼是由1套屈光器(1个角膜和1个晶锥)、6至8个小网膜细胞及其特化产生的视杆和基细胞等几部分组成。晶体周围及小网膜色素细胞内均含有丰富的色素颗粒。(3)小眼整体纵切显示,其上、下段色素颗粒分布相对较多,中段分布较少。(4)明、暗适应状态对小眼的色素颗粒分布有影响,性别对其分布无明显影响。明适应状态下,其色素颗粒较均匀地分布于视杆两侧上下,暗适应状态时色素颗粒则主要分布在视杆部位的上侧,显示其具有一定的重叠眼性质;而在相同的明、暗适应状态下其雌、雄成虫复眼的色素颗粒分布间无明显差异。     

Regional differences in a nematoceran retina (Insecta,Diptera)

Summary The compound eye of Psychoda cinerea comprises two types of ommatidia, arranged so as to divide the retina into distinct dorsal and ventral regions. The P-type ommatidium, in the ventral part of the eye, differs fundamentally from the other dipteran ommatidia so far described, and is regarded as a primitive ommatidium. The acone dioptric apparatus is the same in both types, with a spherical lens and four Semper cells, the processes of which expand below the rhabdom to form a ring of pigment sacs. Only the distal region of the rhabdom is surrounded by a continuous ring of screening pigment, formed by 2 primary and 12–16 secondary pigment cells. The highly pigmented retinula cells penetrate the basement membrane proximally at about the level of their nuclei; in this region they are separated from the hemolymph by glial elements. The rhabdomeres R1–6 are fused to form a tube. The two types of ommatidia are defined by the arrangement of the retinula cells R7/8: in the T type the central rhabdomeres are one below the other, in the usual tandem position, whereas in the P type only R8 is central, with R7 in the peripheral ring. In the proximal region of the retina, retinula cells with parallel microvilli in neighboring ommatidia are joined in rows by lateral processes from the R8 cells. All the rhabdomeres are short and not twisted, which suggests that the retinula cells are highly sensitive to direction of polarization. The eye can adapt by a number of retinomotor processes. These findings, together with observations of behavior, imply that the psychodids have well-developed visual abilities.     

The retina of the phalangid,Opilio ravennae,with particular reference to arhabdomeric cells

Summary The retina of the phalangid, Opilio ravennae, consists of retinula cells with distal rhabdomeres, arhabdomeric cells, and sheath cells. The receptive segment of retinula cells shows a clear separation into a Proximal rhabdom, organized into distinct rhabdom units formed by three or four retinula cells, and a Distal rhabdom, consisting of an uniterrupted layer of contiguous rhabdomeres. One of the cells comprising a retinula unit, the so-called distal retinula cell (DRC), has two or three branches that pass laterally alongside the rhabdom, thereby separating the two or three principal retinula cells of a unit. The two morphologically distinct layers of the receptive segment differ with respect to the cellular origin of rhabdomeral microvilli: DRC-branches contribute very few microvilli to the proximal rhabdom and develop extremely large rhabdomeres in the distal rhabdom only, causing the rhabdom units to fuse. Principal retinula cells, on the other hand, comprise the majority of microvilli of the proximal rhabdom, but their rhabdomeres diminish in the distal rhabdom. It is argued that proximal and distal rhabdoms serve different functions in relation to the intensity of incident light.In animals fixed 4 h after sunset, pigment granules retreat from the distal two thirds of the receptive segment. A comparison of retinae of day- and night-adapted animals shows that there is a slight (approximately 15%) increase in the cross-sectional area of rhabdomeral microvilli in dark-adapted animals, which in volume corresponds to the loss of pigment granules from the receptive segment. The length of the receptive segment as well as the pattern and shape of rhabdom units, however, remain unchanged.Each retinula unit is associated with one arhabdomeric cell. Their cell bodies are located close to those of retinula cells, but are much smaller and do not contain pigment granules. The most remarkable feature is a long, slender distal dendrite that extends up to the base of the fused rhabdom where it increases in diameter and develops a number of lateral processes interdigitating with microvilli of the rhabdom. The most distal dendrite portion extends through the center of the fused rhabdom and has again a smooth outline. All dendrites end in the distal third of the proximal rhabdom and are never present in the layer of the contiguous distal rhabdom. Arhabdomeric cells are of essentially the same morphology in day- and night-adapted animals. They are interpreted as photoinsensitive secondary neurons involved in visual information-processing that channel current collected from retinula cells of the proximal rhabdom along the optic nerve. A comparison is made with morphological equivalents of these cells in other chelicerate species.     

Daily changes of structure,function and rhodopsin content in the compound eye of the crabHemigrapsus sanguineus

The compound eye of the crab hemigrapsus sanguineus undergoes daily changes in morphology as determined by light and electron microscopy, both in the quantity of chromophore substances studied by HPLC and in visual sensitivity as shown by electrophysiological techniques. 1. At a temperature of 20 degrees C, the rhabdom occupation ratio (ROR) of an ommatidial retinula was 11.6% (maximum) at midnight, 8.0 times larger than the minimum value at midday (1.4%). 2. Observations by freeze-fracture revealed that the densities of intra-membranous particles (9-11 nm in diameter) of rhabdomeric membrane were ca. 2000/microns 2 and ca. 3000/microns 2 for night and daytime compound eyes, respectively. 3. Screening pigment granules migrated longitudinally and aggregated at night, but dispersed during the day. Reflecting pigment granules migrate transversally in the proximal half of the reticula layer i.e. cytoplasmic extensions containing reflecting pigment granules squeeze between neighbouring retinula cells causing optical isolation (Fig. 4). Thus the screening pigment granules within the retinula cells show longitudinal migration and radial movement so that the daytime rhabdoms are closely surrounded by the pigment granules. 4. At 20 degrees C, the total amount of chromophore of the visual pigment (11-cis and all-trans-retinal) was 1.4 times larger at night than during the day i.e. 46.6 pmol/eye at midnight and 33.2 pmol/eye at midday. Calculations of the total surface area of rhabdomeric membrane, total number of intra-membranous particles in rhabdomeric membrane and the total number of chromophore molecules in a compound eye, indicate that a considerable amount of chromophore-protein complex exists outside the rhabdom during the day. 5. The change in rhabdom size and quantity of chromophore were highly dependent on temperature. At 10 degrees C both rhabdom size and amount of chromophore stayed close to daytime levels throughout the 24 hours. 6. The intracellularly determined relative sensitivity of the dark adapted night eye to a point source of light was about twice as high as the dark-adapted day eye. Most of the increase in the sensitivity is attributed primarily to the effect of reflecting pigment migration around the basement membrane and, secondarily, to the changes in the amount and properties of the photoreceptive membrane. The results form the basis of a detailed discussion as to how an apposition eye can function possibly as a night-eye.     

蟋蟀视觉系统的解剖结构与生理机能

蟋蟀视觉系统由单眼、复眼、视叶三部分组成。蟋蟀的单眼为背单眼,由角膜、角膜生成细胞、视网膜等组成,是提高昆虫复眼所感知的视觉刺激的兴奋水平部位;复眼是最主要的视觉器官,由角膜、晶锥、感杆束和网膜细胞、基膜组成,是光电转导和视觉级联反应的中心;视叶由神经节层、外髓和内髓组成,是视觉神经系统的中心。     

Visual behaviour and the structure of dark and light-adapted larval and adult eyes of the New Zealand glowworm Arachnocampa luminosa (Mycetophilidae: Diptera)

Both larval and adult New Zealand cave glowworms exhibit reactions to light; their photoreceptors must, therefore, be regarded as functional. The two principal stemmata of the larva possess large biconvex lenses and voluminous rhabdoms. Approximately 12 retinula cells are present. In light-adapted larvae the diameter of the rhabdom is 8 μm and that of an individual microvillus is 49.5 nm. Dark-adapted eyes have rhabdoms that measure 14 μm in cross section and microvilli with an average diameter of 54 nm. The compound eye of the adult comprises approximately 750 ommatidia, each with a facet diameter of 27–28 μm. A facet is surrounded by 1–6 interommatidial hairs which are up to 30 μm long. The interommatidial angle is 5.5°. Cones, consisting of 4 crystalline cone cells, are of the ‘acone’ type. Pigment granules in the primary pigment cells are twice as large as those of the retinula cells which measure 0.6–0.75 μm in diameter. The rhabdom is basically of the dipteran type, i.e. six open peripheral rhabdomeres surround 2 central rhabdomers arranged in a tandem position. The microvilli of cells 1–6 and cell 8 have diameters ranging from 68 to 73 nm, but those of the distally-located central rhabdomere 7 are 20% larger. This is irrespective of whether the eye is dark or light-adapted. In the latter the cones are long and narrow, the screening pigment granules closely surround the rhabdomeres, and the rhabdom is less voluminous than that of the dark-adapted eye.     

Fine structure of the compound eye of Porcellio scaber in light and dark adaption.

The compound eyes of the terrestrial isopod Porcellio scaber comprises about 20 ommatidia. The dioptric apparatus of each ommatidia includes a biconvex corneal lens and a spherical crystalline cone that is secreted by two cone cells. The closed rhabdom is formed by the microvillar extensions of seven pigmented retinula cells and one apical eccentric cell. All retinular axons exit the eye in one bundle. During dark-adaption pigment granules in the retinula cells rapidly withdrew from around the rhabdom and the cell periphery, and migrated basally. Rhabdoms thickened because of movement of the microvilli, and mitochondria moved medially and basally. During light adaption these processes were reversed. Multivesicular bodies became less numerous and rough endoplasmic reticulum and ribosomes proliferated during the initial stages of light adaption.     

Description of intracerebral ocelli in two species of North American crayfish: Orconectes limosus (Cambaridae) and Pacifastacus leniusculus (Astacidae)

Abstract. Among malacostracan crustaceans, intracerebral ocelli were first discovered in Isopoda, but they have been more recently reported from a crayfish ( Cherax destructor ) and a sandhopper ( Talitrus saltator ). This electron microscopic study increases the number of crayfish taxa in which intracerebral ocelli are now known to occur by two: Astacidae and Cambaridae. These photoreceptors are always integrated into the anteromedio-dorsal part of the brain and are not visible externally. Each ocellus is made up of 4–5 photoreceptor cells and is characterized by the presence of a fused rhabdom. The occurrence of different kinds of lysosomes in the cytoplasm is indicative of metabolic activity and perhaps membrane turnover. One typical feature of crayfish ocelli is their extraordinary variability in number. This trait is exemplified by individuals of Pacifastacus leniusculus , where as many as 14 ocelli were identified in a single brain. The arrangement of the ocelli is often not symmetrical with regard to the brain's midline and the ocelli always lack dioptric structures. Thus, it is difficult to see how they are involved in image formation. However, further research is needed to determine the precise role of these "hidden" receptors.     

Intracerebral ocelli in an amphipod: extraretinal photoreceptors of the sandhopper Talitrus saltator (Crustacea, Amphipoda)

Abstract. No morphological clues on the amphipod head indicate the existence of ocelli. However, as in several isopod species studied so far, two rudimentary photoreceptors are integrated into the medio-dorsal part of the brain. This electron microscopical study of the photoreceptors is the first report on the presence of ocelli in amphipods. Each ocellus is made up of 3 receptor cells which contribute to the formation of a photoreceptive surface (the rhabdom) formed by tightly packed microvilli. The rhabdoms are twisted and irregular in outline. Membrane turnover is suggested by the presence of different kinds of lysosomes. Lacking dioptric lenses, these photoreceptors are not likely to be involved in image formation but may function as appraisers of ambient light intensity. Physiological and behavioral studies will, henceforth, have to take into account these unexpected ocelli, which may represent remnants of the naupliar eye.