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Notes: Summary In the early pupal stage (48–60 h after moulting) of the leaf-cutter bee Megachile rotundata, the pairs of centrioles in the retinula cells are proximal to the nucleus, far away from the rhabdom which is developed only in distal areas at this stage. The centrioles are aligned perpendicular to another with the distal centriole parallel to the longitudinal axis of the ommatidium, or are in transitional positions tending to a tandem. According to earlier investigations (Wachmann et al., 1973) this is the final stage. Once this position is obtained the first root fibrils appear and unite in a root fibre as progress towards the imaginal cell stage continues. It is still not known at what stage Tubuli or fibrils extending in a distal direction first appear. The results indicate a high probability that the centrioles involved in mitotic cell divisions are identical with those transformed to ciliary structures in the imaginal cell stage. It was not possible to demonstrate any connexion between the centrioles and the developing microvilli of the rhabdomeres.

Notes: Summary Ommatidia in the dorsal part of the compound eye in female Megachile (a solitary bee) were studied with the electron microscope. The crystalline conesubstance of the Semper (type cells eucone) borders a wide area of the cornea, which probably implies an improved optical system compared with other eucone eyes. The four processes of the Scraper cells extend to the basement membrane, where they enlarge and are filled with screening pigment. The iris pigment cells end distally by impinging on a small area of the cornea and (unlike other ommatidia with an eucone form of crystalline cone) they do not overlap the corneal cells. The retinal pigment cells are entirely filled with pigment granules. A basal pigment cell as described in each ommatidium in Apis does not occur in Megachile. Instead, one finds the basal swellings of the Semper cell processes mentioned above. Usually the retinula consists of nine retinular cells arranged in a closed rhabdom. In the distal part of the ommatidium, this rhabdom is built by microvilli of the retinular cells number 1 and 5, aligned in one direction each perpendicular to the next. These two rhabdomeres are bordered on one side by the rhabdomeres of cell 2–4, and on the other side by those of cells 6–8. Again, these rhabdomeres are all aligned in one direction perpendicular to that of cell 1 and 5. Further down towards the base, there is an area in which the rhabdomeres of the retinular cells 2–4 and 6–8 face another as mentioned above, whereas those microvilli belonging to cell 1 and 5 seem to be forced away towards the periphery of the rhabdom. In addition to common organelles, both the pigment cells and Semper cells contain centrioles arranged at an angle or in tandem. In the retinular cells, they correspond to the basal bodies of cilia, and they give rise to tubules (sometimes striated fibrils are found). However, towards to base they give rise to striated fibrils which unite in a root fibre. — The results are discussed and compared with those known of Apis.

Notes: Summary The entire rhabdom of the ommatidia in dorsal and ventral eyes (“superposition eyes”) ofGyrinus proceeds from the base of the crystal cone to the vicinity of the basal membranewithout any interruption. However, a differentiation of three distinguishable sections can be recognized. The electronmicroscopic results presented in this paper show that the distal section of the ommatidial retinulae contain the rhabdomere of cell 1 only. The proximal section is occupied by the basal rhabdom of cells 2–7, further proximal by the much smaller rhabdomere of cell 8. Concerning a probable ability to use the pattern of polarized skylight for orientation, the alignment of the microvilli as well in one ommatidium as across large areas of the eye is of special interest. In the ventral eye the microvilli-alignment of cells 1–7 shows one direction over large ommatidial areas, respectively. This only partially comes true for the alignment in the dorsal eye, since there also occur twistings. As a consequence microvilli of corresponding cells may point towards different directions. In both eye types the rhabdomeres of neighbouring cells 8 can point towards different directions. Sometimes microvilli of one cell 8 gather in tufts with axises different directions. There are substantial differences in both the ventral and dorsal eye concerning the rhabdomere of cell 1. The relations of alignment of rhabdomeres described in this paper are subject for a discussion on a probable analysis of polarized light byGyrinus.

Notes: Abstract  In its plesiomorphic state the insect ommatidium consists of eight retinula cells forming a fused rhabdom. It has long been observed that, in contrast to this pattern, Heteroptera have open rhabdoms. However, there has so far been no comprehensive and comparative study of heteropteran ommatidia. For this reason, we investigated the rhabdom structure in 36 species from all higher groups of Heteroptera, as well as from Coleorrhyncha and Auchenorrhyncha as outgroup representatives. In addition we surveyed the data of earlier authors, which brings the number of examined species to a total of more than 70. All examined Heteroptera do have open rhabdoms, with a system of six peripheral and two central rhabdomeres. Outgroup comparison shows that the open rhabdom is an autapomorphy of the Heteroptera. As for the rhabdom structure within the Heteroptera, we found further autapomorphic patterns in Corixidae (Nepomorpha), Gerromorpha, and Leptopodomorpha. Finally, the Cimicomorpha and Pentatomomorpha share a special pattern of the two central rhabdomeres, which we call V-pattern. This is a new synapomorphy of these two taxa.

Notes: Summary The eyes in 55 species of 8 subfamilies of long-horned beetles (Cerambycidae) have been examined ultrastructurally. An eye consists of acone ommatidia of which each is assembled by a bi-convex corneal lens, 4 Semper-cells, 8 retinula cells, 2 primary pigment cells, and of a larger and variable number of secondary pigment cells. The differently arranged rhabdomeres of the — as a rule — open rhabdoms can be summed up to two basic patterns: In the case of the basic pattern 1 the central rhabdomeres R 7/8 are completely isolated from the peripheral rhabdomeres R 1–6. As to the basic pattern 2 the central rhabdomeres R 7/8 are structurally attached to the peripheral rhabdomere arrangement through R 1 and R 4. Due to different directions of the microvilli in R 7 and R 8 there occur several rhabdomeral shapes. Furthermore, within some taxa partially fused rhabdoms are present; in one species the fusion is even complete. Nevertheless, a derivation from an open rhabdom with reference to one of the basic patterns is always possible due to a clear homologous comparison of the anticipating retinula cells. The successfully answered question upon a taxon-specifity of the basic patterns and the rhabdomeral shape allows statements as to the value of these ultrastructural patterns for a phylogenetic argumentation. In Cerambycidae the distinct and not uniform arrangement of these patterns and shapes within lower, closer related taxa represents the occurrence of convergencies (as compared to the extraordinarily similar rhabdoms in Chrysomelidae, Wachmann, 1977, which receive in this paper a further support as to their subfamiliar specification). However, these convergencies are demonstrable through the phylogenetic system only. Thus, patterns of open rhabdoms can only be used as more or less additional indices on a monophyly of groups which already has been proved by means of other characteristics. In spite of an extreme conformity within different taxa rhabdomeral characteristics solely are not appropriate enough in order to separate monophyletic groups. The ultrastructural investigations give a good basis as to the interpretation of the function of the different rhabdoms. However, the question remains not answered whether there exist equal or unequal strategies of circuits within the lamina and medulla.

Notes: 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 μm 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.

Notes: Summary A large single “cornea” is situated on the frontal side of the naso of Microcaeculus. Caudally and nearly coaxial to the cornea separated by a hemolymphatic cavity, are the two median eyes on the other side of the naso. They face the bases of the cheliceres, directed caudally. The cuticle of the eye attains a thickness of up to only 0.24 μm. Sensory cells protrude from the eye cup in a dorsal direction delivering axons of different diameters bent caudally toward as yet undetermined centers. Each eye consists of 6 retinula cells, covered by a thin epithelial layer, and of an undetermined number of sheath cells. Different zones can be distinguished schematically in the sensory cells: 1. Rhabdomere Zone. Directly beneath the cuticle and the cuticle-forming cells, rhabdomeres are spread superficially; their corresponding plasmatic regions, also located here, contain much smooth- and rough-surfaced endoplasmic reticulum (ER), some multivesicular bodies, mitochondria, centrioles, and α-glycogen. 2. Microtubuli Zone. This zone is characterized by many microtubules. Few rough-surfaced ER, but many mitochondria, are present in this zone; voluminous ER cisterns are to be found placed in the cell area facing the hemolymphatic cavity. 3. Nucleus Zone. Due to an increased cell volume in this zone, the eyes overlap over a large area. In the sensory cells a conspicuous massing of glycogen rosettes, as well as several organelles, is to be found. 4. Axon Zone. The axons are of varied diameter (0.7–1.8 μm). Large amounts of glycogen are found only in thicker axons, cross-structured by single smooth ER-cisterns. Electron-microscopic investigations confirmed the findings of Coineau (1970). Additional probabilities are presented and discussed in regard to other functions of these eyes. As to the structure of the eyes, a perception of differences in light intensity is probable. Image vision seems an impossibility, as only 6 retinula cells exist in each eye. However, a certain “perception of light direction” may be possible since the field of view is limited by the body and its dorsal ledge.

Notes: Summary Eyes of the Coleoptera previously examined possess fused rhabdoms in all but a few species that have open rhabdoms consisting of 2 central and 6 peripheral rhabdomeres. Recent investigation of more than 70 species from about 20 families (with a total of 150,000 species) led to the conclusion that nearly one-half of all Coleoptera species possess the open-rhabdom type of eye. All of these species belong to the Cucujiformia (composed of the 5 superfamilies Cleroidea, Lymexyloidea, Cucujoidea, Chrysomeloidea and Curculionoidea, sensu Crowson, 1967), and — until now — no species of this group has been found to have fused rhabdom eyes. The open rhabdomic eye is therefore considered a synapomorphous feature (sensu Hennig, 1966) of the Cucujiformia, and this taxon is regarded as a monophyletic. From electronmicroscopic examinations of 41 Chrysomelidae species from 9 subfamilies and of 18 Cerambycidae of 3 subfamilies, the position of the central rhabdomeres (R 7, 8) relative to the peripheral rhabdomeres (R 1–6) and the direction of microvilli in the central rhabdomeres were chosen for comparison. The central rhabdomeres were found to be fused, laterally, to R 1 and R 4 in all of the species from the subfamily Chrysomelinae, but no such fusion was found in any species of the other 8 subfamilies of the Chrysomelidae, nor in any of the Cerambycidae or Bruchidae examined. Microvilli of R 7 and R 8 are parallel in Donaciinae, Criocerinae, Eumolpinae, and many Chrysomelinae, and in Lepturinae, Cerambycinae and Lamiinae (Cerambycidae) and in Bruchidae. Microvilli of both rhabdomeres are aligned in several directions in the Galerucinae, Hispinae, Clytrinae, but only inPhytodecta of the Chrysomelinae, and characteristic differences in the arrangement of microvilli were recognized among these Chrysomelidae. Microvilli were parallel in one of the central rhabdomeres, but aligned in two or more directions in the other, in species of Megalopodinae, Orsodacninae, but only inTimarcha among Chrysomelinae, and again the arrangement of microvilli was characteristic of the subfamilies of these Chrysomelidae (exception: Chrysomelinae). The central rhabdomere systems possessing microvilli of only one direction, but not fused at any level of the ommatidia with peripheral rhabdomeres, are considered symplesiomorphous for this superfamily. This simple arrangement of microvilli in many diverse groups of Chrysomelidae, Cerambycidae and Bruchidae may be regarded as the basic pattern from which the different arrangements in other subfamilies were derived. Similarities in arrangement of the microvilli (among taxa of different families) are considered to be convergences. — The results are also discussed with a view to functional properties of the rhabdomeres.