The nucleolar fibrillar centres in various cell types in vivo or in vitro

Summary The compound eye of male (haploid) Xyleborus ferrugineus beetles was examined with scanning and transmission electron microscopy. The eye externally consists of ca. 19 to 33 facets. Each ommatidium is composed of a thickly biconvex lenslet with about 50 electron dense and rare layers, but at the junction area between two lenslets there are only about 35 to 37 layers that can be distinguished. A very short (3.4–4.0 m) acone type crystalline cone is located directly beneath the lenslet. Each ommatidium is surrounded by pigment cells, and pigment granules also appear throughout the cytoplasm of the retinular cells. Some pigment granules are even present below the basement membrane. There are 8 retinular cells. The rhabdomeres of 2 centrally situated photoreceptor cells fuse into a rhabdom which is enveloped by the rhabdomeres of 6 peripheral retinular cells. The rhabdomeres of the 6 peripheral retinular cells join laterally to form a rhabdomeric ring around the central rhabdom. No tracheation was observed among the retinular cells. Virus-like particles are evident near the nucleus in each Semper cell of the crystalline cone.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.     

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.     

Degeneration of the compound eye of the termite Neotermes jouteli (Isoptera) in darkness during the phase of reproduction

Summary Long-term light deprivation of the royal pair of Neotermes jouteli during the phase of reproduction leads to a dramatic change in the organization within the compound eye. In a swarming alate, investigated with scanning and transmission electron microscopy, the eye consists of about 200 ommatidia. No differences between male and female eyes are observed. Each ommatidium is composed of a biconvex cornea, a cone of the eucone type, and a rhabdom which is located directly beneath the Semper cells. The rhabdom consists of eight rhabdomeres which are fused along the ommatidial axis. In the central part of the compound eye the rhabdom measures roughly 20 m in length. Concealed life of the imagines causes a dismantling of the cone and the rhabdom until complete destruction. This is accompanied by an increase in the number of pigment granules and a decrease in the number of mitochondria.     

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。     

Morphology of the compound eye of the giant deep-sea isopod Bathynomus giganteus

The structural organization of the compound eye of the largest known isopod, Bathynomus giganteus, is described from four specimens maintained in the laboratory for as long as two months. Living specimens have not previously been available for study. The two triangular compound eyes measure about 18 mm on the dorsal edge and are separated by an interocular distance of 25 mm. They face forward and slightly downward and may have significant overlap in visual fields. Each eye contains about 3,500 ommatidia in animals of body lengths from 22.5 cm to 37.5 cm. The packing of ommatidia is not uniform across the retina, but is nearly hexagonal in the dorsal central region and nearly square in the ventral and lateral periphery. The dioptric elements in each ommatidium consist of a laminar cornea, which is flat externally and convex internally, and a bipartite crystalline cone. Sometimes seven and sometimes eight retinular cells closely appose the proximal tip of the cone and bear the microvilli of the rhabdom. Proximal to the rhabdom the retinular cells form thin pillars near the periphery of the ommatidium, and the central portion along the optic axis at this level is occupied by interstitial cells that contain massive arrays of clear vesicles thought to serve as reflective elements. The arhabdomeral segments of the retinular cells and the interstitial cells rest on a basement membrane. Within each ommatidium the basement membrane has two extensions with cylindrical cores and thin sheets of dense material and collagen-like filaments. These sheets occupy spaces between adjacent interstitial cells up to the level of the rhabdomeral segments of the retinular cells. Arrays of pigment cells with relatively weak light-screening properties separate adjacent ommatidia. Animals were fixed both in light within a week of being brought from depth into daylight, and after 2 months of maintenance in constant darkness following such daylight exposure. In both cases, microvilli of the rhabdom were severely disrupted and the retinular cytoplasm contained numerous multivesicular bodies. Exposure to natural daylight appears to cause irreversible structural damage to the photoreceptors of these animals.     

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.     

Organisation of the compound eye of a tipulid fly during the day and night

Summary The ultrastructure of the compound eye of the Australian tipulid fly,Ptilogyna spectabilis, is described. The ommatidia are of the acone type. The rhabdom corresponds to the basic dipteran pattern with six outer rhabdomeres from retinular cells 1–6 (R1-6) that surround two tiered central rhabdomeres from R7 and 8. Distally, for about 8 m, the rhabdom is closed. For the remainder, where the rhabdomere of R8 replaces that of R7, the rhabdom is open, and the rhabdomeres lie in a large central ommatidial extracellular space. In the proximal two thirds of the rhabdom, the central space is partitioned by processes from the retinular cells so that the individual rhabdomeres are contained in pockets.At night the rhabdom abuts the cone cells, but during the day it migrates some 20 m proximally and is connected to a narrow (1–2 m) cone cell tract. This tract is surrounded by two primary pigment cells, which occupy a more lateral position at night and thus act like an iris. Pigment in secondary pigment cells also migrates so as to screen orthodromic light above the rhabdom during the day. Between midday and midnight, the rhabdom changes in length and cross-sectional area as a result of asynchrony of the shedding and synthetic phases of photoreceptor membrane turnover. The effects of these daily adaptive changes on photon capture ability are discussed with regard to the sensitivity of the eye.     

螺旋粉虱成虫的复眼形态及其内部结构

采用扫描电镜和组织切片法,观察了螺旋粉虱Aleurodicus dispersus Russell成虫复眼的形态及其显微结构。结果表明,螺旋粉虱复眼半球状,呈“∞”形分布于头部两侧,单个复眼约由253个小眼组成;各小眼面微凸,复眼中心区域小眼多为规则的六边形,密集排列似蜂窝状;近背区边缘小眼多为五边形或近圆形,小眼排列疏松,且少量相邻小眼的间距较大。雌、雄复眼小眼面积约为85μm2。单个小眼由角膜、晶体、网膜细胞及其特化产生的视杆和基细胞等几部分组成。晶体有四个晶锥细胞构成,晶体、视杆周围和色素细胞内均含有大量的色素颗粒。螺旋粉虱的复眼属于并置复眼。光、暗条件下,小眼的色素颗粒分布有所不同。光适应条件下,色素颗粒较均匀地分布于视杆上下两侧;暗适应状态下,色素颗粒则主要分布在视杆上侧和晶体下侧。而在相同的明、暗适应条件下,性别对色素颗粒的分布无显著影响。     

The compound eye of<Emphasis Type="Italic"> Scutigera coleoptrata</Emphasis> (Linnaeus, 1758) (Chilopoda: Notostigmophora): an ultrastructural reinvestigation that adds support to the Mandibulata concept

The lateral compound eye of Scutigera coleoptrata was examined by electron microscopy. Each ommatidium consists of a dioptric apparatus, formed by a cornea and a multipartite eucone crystalline cone, a bilayered retinula and a surrounding sheath of primary pigment and interommatidial pigment cells. With reference to the median eye region, each cone is made up of eight cone segments belonging to four cone cells. The nuclei of the cone cells are located proximally outside the cone near the transition area between distal and proximal retinula cells. The connection between nuclear region and cone segment is via a narrow cytoplasmic strand, which splits into two distal cytoplasmic processes. Additionally, from the nuclear region of each cone cell a single cytoplasmic process runs in a proximal direction to the basement membrane. The bilayered rhabdom is usually made up of the rhabdomeres of 9–12 distal retinula cells and four proximal retinula cell. The pigment shield is composed of primary pigment cells (which most likely secrete the corneal lens) and interommatidial pigment cells. The primary pigment cells underlie the cornea and surround, more or less, the upper third of the crystalline cone. By giving rise to the cornea and by functioning as part of the pigment shield these pigment cells serve a double function. Interommatidial pigment cells extend from the cornea to the basement membrane and stabilise the ommatidium. In particular, the presence of cone cells, primary pigment cells as well as interommatidial pigment cells in the compound eye of S. coleoptrata is seen as an important morphological support for the Mandibulata concept. Furthermore, the phylogenetic significance of these cell types is discussed with respect to the Tetraconata.     

FINE STRUCTURE OF THE RETINULAE IN THE COMPOUND EYE OF THE HONEY-BEE

The retinula of the compound eye of the worker honey-bee has been examined with the electron microscope. The rhabdom lies on the ommatidial axis; it is usually cylindrical in shape, about 3 to 4 µ in diameter, and lacks an axial cavity. Cross-sections show it to be four parted, although it is formed from eight retinular cells (Figs. 2, 3). Each quadrant of the rhabdom consists of a closely packed parallel array of tubules with long axes perpendicular to the axis of the rhabdom. The tubules in adjacent quadrants of the rhabdom are mutually perpendicular. At the distal end of the ommatidium these tubules are seen to be microvilli of the retinular cells. Immediately surrounding the rhabdom, the cytoplasm of the retinular cells contains a membranous endoplasmic reticulum which is oriented approximately radially with respect to the axis of the ommatidium. Farther away from the rhabdom the cytoplasm contains numerous mitochondria.     

The Fine Structure of the Compound Eye of Tanais cavolinii Milne-Edwards (Crustacea: Tanaidacea)

Abstract The compound (apposition) eyes of Tanais cavolinii are not well developed: the number of ommatidia is small and there are certain irregularities in structure. The refractive components are formed by the cornea and the cone. The latter is built up by two cone cells. In addition, there are two accessory cone cells confined to the distal part of the cone. The eight pigmented retinular cells extend from the cornea to the basement membrane. Proximal to the cone, they form a fused continuous rhabdom, which in cross section has a rectangular outline. In the middle part of the rhabdom, the microvilli are arranged perpendicular to the long axis of the rhabdom when seen in cross section. The microvilli outside of this area can be arranged either parallel or perpendicular to the microvilli of the middle part. Other irregularities occur in the ommatidium, e.g. the position of the retinular cell nuclei, which are found at different levels. Extensions from the cone cells fuse and form a mesh proximal to the rhabdom. Between the mesh and basal lamina is a basal cell type enveloping the proximal parts of the retinular cells and their axons. These cells also form the basal lamina, which delimits the compound eye from the haemocoel. No special pigment cells are present in the compound eye of Tanais cavolinii.     

Fine structure of light- and dark-adapted eyes of desert ants,Cataglyphis bicolor (Formicidae,Hymenoptera)

Among ants, Cataglyphis bicolor shows the best performance in optical orientation. Its eye is of the apposition type with a fused rhabdom. Morphological studies on the general struture of the eye as well as the effect of light have been carried out with transmission and scanning electron microscopy. An ommatidium is composed of a dioptric apparatus, consisting of a cornea, corneal process and a crystalline cone, the sensory retinula, which is made up of eight retinula cells in the distal half and of an additional ninth one in the proximal half. The ommatidia are separated from each other by two primary pigment cells, which surround the crystalline cone and an average of 12 secondary pigment cells, which reach from cornea to the basement membrane. The eye of Cataglyphis bicolor possesses a light intensity dependent adaptation mechanism, which causes a radial and distal movement of the pigment granules within the retinula cells and a dilatation of cisternae of the ER along the rhabdom. Until now, no overall order in arrangement of retinula cells or direction of microvilli has been found from ommatidium to ommatidium. Such an order, however, must exist, either on the retina or the lamina level, since we have proven the ant's capacity for polarized light analysis.     

Ultrastructure of the larval eye of the scorpionfly Panorpa dubia (mecoptera: Panorpidae) with implications for the evolutionary origin of holometabolous larvae

The evolutionary origin of holometabolous larvae is a long‐standing and controversial issue. The Mecoptera are unique in Holometabola for their larvae possessing a pair of compound eyes instead of stemmata. The ultrastructure of the larval eyes of the scorpionfly Panorpa dubia Chou and Wang, 1981 was investigated using transmission electron microscopy. Each ommatidium possesses a cornea, a tetrapartite eucone crystalline cone, eight retinula cells, two primary pigment cells, and an undetermined number of secondary pigment cells. The rhabdomeres of the eight retinula cells form a centrally‐fused, tiered rhabdom of four distal and four proximal retinula cells. The rhabdomeres of the four distal retinula cells extend distally into a funnel shape around the basal surface of the crystalline cone. Based on the similarity of the larval eyes of Panorpidae to the eyes of the hemimetabolous insects and the difference from the stemmata of the holometabolous larvae, the evolutionary origin of the holometabolous larvae is briefly discussed. Morphol., 2012. © 2012 Wiley Periodicals, Inc.     

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.     

Further studies on the development of the eye of Drosophila melanogaster. I. The ommatidia

Electron microscope observations on the differentiating Drosophila eye show an extensive proliferation of parallel arrays of microtubules at periods preceding, or coinciding with, alterations in cellular morphology. In the retinular cells they are aligned in the direction of elongation and close to the developing rhabdomeres, forming a cylinder around the central ommatidial axis. At a later stage, in the cone cells, they are aligned in the direction of cellular contraction. Thus as in other developing systems microtubules appear to be directly involved in the morphogenesis of the Drosophila eye. In the retinular cells they gradually disappear during elongation, whereas they persist in the cone cells. The pigment cells contain few of these structures. The distribution of two types of specialised cell attachments, adhering zones and septate desmosomes is discussed in relation to intercellular morphogenesis and communication. The rhabdomeres originate from infoldings of the plasma membrane which later grow out into typical microvilli. Unusul cytoplasmic granules are described in the pigment cells of early pupae.     

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.     

南五台蝎蛉成虫复眼的超微结构

采用扫描电镜和组织切片法,观察南五台蝎蛉Panorpa nanwutaina Chou成虫复眼的超微结构。南五台蝎蛉复眼近半椭球形,包括1500～1600个小眼。小眼表面光滑,由角膜、晶体、2个初级和12个次级色素细胞、视杆、以及基膜组成。角膜为多层片状纤维结构;晶体含有4个晶锥细胞;视杆由若干个视网膜细胞组成。晶体、视杆周围、和色素细胞内含有大量的色素颗粒,基膜两侧也有色素颗粒分布。南五台蝎蛉的复眼属于并列像眼。与普通蝎蛉P.communis L.小眼的次级色素细胞数目不同。讨论了南五台蝎蛉角膜的功能以及感觉毛和次级色素细胞在分类中的作用。     

灰茶尺蠖成虫复眼的超微结构及其明暗适应中的变化

【目的】明确灰茶尺蠖Ectropis grisescens成虫复眼的超微结构及其明暗适应中的变化,探究其调光机制。【方法】采用超景深显微镜测定了灰茶尺蠖成虫复眼的小眼数量、间角、直径和曲率半径等外部参数,并通过组织切片、光学显微镜和透射电子显微镜等技术观察了复眼的内部超微结构;通过光学显微镜观察了灰茶尺蠖成虫复眼在明暗环境中分别适应2 h后晶锥结构及色素颗粒的位置变化。【结果】灰茶尺蠖成虫复眼呈半球形,雌、雄虫单个复眼分别有2 502±105和3 123±78个小眼。小眼自远端至近端由角膜、晶锥、透明区构成的屈光层和由15个视网膜细胞构成的感光层组成。2个初级色素细胞包裹着晶锥,自角膜近端延伸至视网膜细胞核区的远端;每个小眼外围由6个次级色素细胞围绕,自角膜近端延伸至基膜;在透明区内14个视网膜细胞聚集成束(非感杆束),远端与晶锥束末端连接,在感光层内形成闭合型感杆束,延伸至第15个视网膜细胞(基部视网膜细胞)。在明暗适应时,灰茶尺蠖复眼的晶锥细胞间出现开闭,色素颗粒进行纵向位移,以适应外界的光强度的变化。【结论】灰茶尺蠖成虫复眼属于重叠像眼,感杆束为“14+1”模式;屏蔽色素颗粒的移动是其复眼适应外界光强度变化的重要机制。     

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。     

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.