The fine structure of the lateral eyes ofNeocarus texanus Chamberlin and Mulaik, 1942 (Opilioacarida,Acari, Arachnida,Chelicerata)

Summary Neocarus texanus, a primitive mite, bears two pairs of eyes, which are principally similar in ultrastructure. Each eye is covered externally by a cuticular cornea. It is underlain by flat sheath cells which send extensive processes into the retina. The retina is composed of distal and proximal cells. The 20 distal cells of the anterior eye are inversely orientated and form 10 disc-like rhabdoms. They represent typical retinula cells. Each rhabdom encloses the dendritic process of a neuron, the perikaryon of which is located outside the retina (proximal cells). The significance of this cell is not known. The retina is underlain by a crystalline tapetum. In the posterior eye 14 retinula cells form 7 rhabdoms in an arrangement similar to the anterior eye. The eyes of one side of the body are located within a capsule of pigment cells. Together the axons of the distal and proximal cells form the two optic nerves, one on each side of the body. The optic nerves leave the eyes anteriorly and terminate in two optic neuropils located in the brain.From structural evidence it is concluded, that the resolution of the eyes must be rather low.The peculiar proximal cells have not been observed previously in Acari. They probably resemble at best the eccentric cells and arhabdomeric cells of xiphosurans, scorpions, whip-scorpions and opilionids. Also, inverse retinae and tapeta of the present type have not been found in Acari until now, but are present in other Arachnida. Thus the eyes ofNeocarus texanus evidently represent a unique type within the Acari.     

Feinstruktur des Komplexauges der Roten Waldameise,Formica polyctena (Hymenoptera,Formicidae)

Zusammenfassung Die Analyse der Feinstruktur des Komplexauges der Ameise Formica polyctena ergab, daß der dioptrische Apparat der insgesamt 750 Ommatidien aus einer lamellierten Cornealinse und einem euconen Kristallkegel besteht. Zwei Hauptpigmentzellen umgeben schalenförmig den Kristallkegel, 8 Nebenpigmentzellen schirmen das Ommatidium in seiner ganzen Länge von der Cornea bis zur Basalmembran ab. Jedes Ommatidium besteht in seinem distalen Teil aus 8 Retinulazellen, 2 gegenüberliegenden schmalen und je 3 gegenüberliegenden großen Sehzellen. Weiter proximal tritt eine 9. Retinulazelle hinzu. Die Mikrovillisäume der Sehzellen verschmelzen zu einem zentralen Rhabdom. Im distalen Teil sind die Mikrovilli in 3 Richtungen angeordnet. Es wird im besonderen die Orientierung der Mikrovilli zur Augenlängsachse und zur Ommatidien-Symmetrieachse untersucht. Auch die 9. Sehzelle bildet Mikrovilli. Das Rhabdom endet an 4 basalen Pigmentzellen.Auf den Mikrovillisaum folgt im Querschnitt des dunkel adaptierten Ommatidiums ein Kranz von großen intrazellulären Vakuolen. Die anschließende cytoplasmatische Zone der Retinulazellen enthält viele Pigmentgranula und Mitochondrien; multivesikuläre und multilamelläre Körper sowie Golgiapparate treten nur selten auf. Die funktionelle Bedeutung des Ommatidienaufbaues und die Verteilung der Organellen bei Dunkeladaptation werden diskutiert.

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The fine structure of the complex eye of the ant Formica polyctena (Hymenoptera, Formicidae)

Summary The fine structure of the compound eye of the ant Formica polyctena was investigated. The eye consists of a total of 750 ommatidia, each containing a dioptric apparatus of a lamellated cornea lens, a eucone-type crystalline cone, and 8 long pigment cells which surround the ommatidium for its total length, i.e. from the cornea to the basal membrane. Each ommatidium has in its distal portion 8 retinula cells—6 large plus 2 small ones. The retinula cells are arranged in such a way that 3 pairs of large cells, and the one pair of the small cells lie opposite each other. Further proximally, a 9th retinula cell is encountered. The fused, centrally located rhabdom is built up by the microvilli of all nine retinula cells. The rhabdom ends at 4 basal pigment cells. In dark adapted ommatidia, a ring of large intracellular vacuoles is to be seen immediately peripherally to the rhabdom. The outer, cytoplasmic zone of the retinula cells contains many pigment granules and mitochondria; multivesicular bodies, onion bodies and Golgi apparatus are of relatively rare occurrence. The functional significance of the ommatidial structure and the arrangement of the cell organelles in the dark adapted condition are discussed.

Für technische Hilfe danke ich Frau Langer und Frl. Müller, Herrn Prof. H. Markl für die Durchsicht des Manuskripts.     

Comparative ultrastructure of the zoospores of nine species ofNeochloris (Chlorophyta)

Nine species ofNeochloris can be divided into three groups on the basis of comparative ultrastructure of the flagellar apparatus, the cell wall and the pyrenoid of zoospores. In Group I,N. wimmeri andN. minuta, zoospores are thin-walled, pyrenoids are penetrated by stromal channels, and the basal bodies are in the clockwise absolute orientation and connected by the distal and two proximal fibers. In Group II,N. aquatica, N. vigenis, N. terrestris, N. pyenoidosa, andN. pseudostigmatica, zoospores are naked or covered by fuzzy material, pyrenoids are covered by a continuous starch sheath or invaginated by cytoplasmic channels, basal bodies are directly opposed, the distal fiber is differentiated into a ribbed structure at the central region, a striated microtubule-associated component (SMAC) is continuous between opposite two-membered rootlets and connected to the ribbed structure, proximal ends of basal bodies are covered by partial caps, each two-membered rootlet and a basal body are connected by a striated fiber to the X-membered rootlet associated with the opposite basal body, and the basal bodies, when oriented at wide angles, are joined at their proximal ends by core extensions. In Group III,N. pseudoalveolaris andN. cohaerens, zoospores are naked, pyrenoids are traversed by parallel thylakoids, basal bodies are in the counterclockwise absolute orientation and overlapped, and each X-membered rootlet is connected to the end of the opposite basal body by a terminal cap. It is suggested that the genusChlorococcopsis gen. nov. be erected for the Group I species. Group II, which includes the type species,N. aquatica, should be preserved asNeochloris. The group appears to be closely related to the coenobial generaPediastrum, Hydrodictyon, andSorastrum, and to have affinities with the coenocytic generaSphaeroplea andAtractomorpha as well. It is also suggested that the genusParietochloris gen. nov. be erected in thePleurastrophyceae for the species of Group III.     

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.     

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.     

Trichodesmium thiebautii; structure of a nitrogen-fixing marine blue-green alga (Cyanophyta)

Summary Trichodesmium thiebautii was collected, as floating bundles composed of uniseriate filaments aligned in parallel, from the Kuroshio waters off Shikoku Island, Japan. The ultrastructure of this alga had basically the same general features as the related speciesT. erythraeum first described byvan Baalen andBrown (1969). InT. thiebautii long electron dense fibers and concentrically lamellated bodies were observed which were either not reported previously, or did not occur inT. erythraeum. The peripheral wall layers were generally typical ofOscillatoria-type blue-green algae, but with a distinctive finely striated outer layer. Thylakoids per cell volume were very sparse compared to most other blue-green algae. Phycobilisomes, apparently hemidiscoidal in shape, typically occurred on the stromal side of the thylakoid surface. Large gas vesicle areas occupied the main volume of the cell, including cells which seemed to be actively growing. The gas vesicle areas were distributed throughout the cell, not only in the cell periphery as inT. erythraeum. Considerable complexity was suggested by the apparent cell compartmentation, particularly because the gas vesicle areas were delimited by one to several thylakoids. Only rarely were the gas vesicle areas traversed by thylakoids. Electron dense fibers (ca. 25 nm diameter) were always observed between the gas vesicles and were usually oriented parallel with them, but they were not rigid appearing as were the gas vesicles. The gas vesicles had a smaller diameter (ca. 45 nm) than most blue-greens. Concentrically lamellated bodies (ca. 1.0 m diameter) were observed in cells of some of the bundles. Each concentric layer was ca. 1.3 nm wide. These concentrically lamellated bodies may be characteristic of older cells. Cylindrical bodies were considerably smaller (ca. 120 nm diameter) and less complex than those reported forT. erythraeum.     

The larval eye of the aeolid nudibranch Trinchesia aurantia (Alder and Hancock)

Summary The larval eye of the aeolid nudibranch Trinchesia aurantia has been investigated at three different stages; in all, the eyes remain closely attached to, and in cellular contact with, the central ganglia. The larval eye is a simplified version of the adult eye in that, the eye and the constituent cells, nuclei, lens, microvilli and pigment granules are all smaller, and the interdigitation between the retinal cells is not developed. The absence of the small cells of the cornea and of the spherical vesicles in the cytoplasm of the sensory cells, is further evidence of the incomplete formation of the eye. The possible origin of the eye of Trinchesia is discussed and compared with that of other gastropods.I am very grateful for the help and guidance of my supervisor Dr. D. A. Dorsett throughout the preparation of this paper. I was sponsored by a grant from the N.E.R.C.     

Basal apparatus behaviour during cellular division (sporulation) in the coccoid green algaChlorosarcina

Summary We studied the basal body cycle (including basal body segregation, duplication, migration, and reorientation) in dividing cells of the colonial coccoid green algaChlorosarcina stigmatica using serial thin sections. Although flagella are lacking, all cells examined possess a rudimentary flagellar apparatus composed of two basal bodies linked by a distal striated fibre, two probasal bodies, and four cruciately arranged microtubular roots (2-4-2-4 type). Basal body segregation occurs at preprophase, during which two half-basal apparatuses (each consisting of one basal body, one probasal body, and a left and a right root) migrate into opposite directions. The segregation axis is defined by the two left roots which remain closely associated during segregation and slide along each other. The segregation axis is parallel to the axis of chromosome separation, and perpendicular to the plane of subsequent cell division. Duplication of basal apparatus components does not occur until telophase when daughter basal apparatuses migrate towards the plane of division. At cytokinesis which is effected by the unilateral ingrowth of a septum, each daughter basal apparatus rotates 90° and becomes associated with the new septum.Abbreviations BA basal (body) apparatus - NBBC nucleus-basal body connector     

Ocellar fine structure inCaenis robusta (Ephemeroptera), Trichostegia minor,Agrypnia varia,andLimnephilus flavicornis (Trichoptera)

Summary Three dorsal ocelli are present inCaenis robusta (Ephemeroptera), Trichostegia minor, Agrypnia varia, andLimnephilus flavicornis (Trichoptera). The dioptric apparatus of the ocelli differs between the four species. InTrichostegia andAgrypnia a biconvex corneal lens is present, inLimnephilus the corneal lens is convexo-concave complemented by an underlying haemocoelic space, whereas a cellular vitreous body is found between the cuticle and the retinal layer in the ephemerid. In the three trichopteroid species the ocelli are surrounded by an array of longitudinally arranged tracheoles; inCaenis a layer of screening pigments is found in this position. In this species the rhabdoms formed by microvilli of neighbouring retinula cells have a randomly arranged meshwork pattern; in the three trichopteroid species the rhabdoms are isolated, built up of four retinula cells. Cells with basally situated nuclei and lamellar extensions between the retinular cells are found in the ocelli ofTrichostegia, Agrypnia, andLimnephilus.     

Functional morphology of the ommatidia in the compound eye of the moth,Antheraea polyphemus (Insecta,Saturniidae)

Summary The fine structure of the superposition eye of the Saturniid moth Antheraea polyphemus Cramer was investigated by electron microscopy. Each of the approximately 10000 ommatidia consists of the same structural components, but regarding the arrangement of the ommatidia and the rhabdom structure therein, two regions of the eye have to be distinguished. In a small dorsal rim area, the ommatidia are characterized by rectangularly shaped rhabdoms containing parallel microvilli arranged in groups that are oriented perpendicular to each other. In all other ommatidia, the proximal parts of the rhabdoms show radially arranged microvilli, whereas the distal parts may reveal different patterns, frequently with microvilli in two directions or sometimes even in one direction. Moreover, the microvilli of all distal cells are arranged in parallel to meridians of the eyes. By virtue of these structural features the eyes should enable this moth not only discrimination of the plane of polarized light but also skylight-orientation via the polarization pattern, depending on moon position. The receptor cells exhibit only small alterations during daylight within the natural diurnal cycle. However, under illumination with different monochromatic lights of physiological intensity, receptor cells can be unbalanced: Changes in ultrastructure of the rhabdomeres and the cytoplasm of such cells are evident. The effects are different in the daytime and at night. These findings are discussed in relation to the breakdown and regeneration of microvilli and the influence of the diurnal cycle. They are compared with results on photoreceptor membrane turnover in eyes of other arthropod species.     

Perianth development inAngophora and the bloodwood Eucalypts (Myrtaceae)

The petals ofAngophora flowers are compound structures consisting of two morphologically distinct components that develop along separate morphogenetic pathways. These two components are also evident in the corolline parts of the bloodwood eucalypts. In occasional flowers ofAngophora and some bloodwoods, several adjacent corolline primordia may become continuous due to interprimordial growth, but the petals are mostly free at anthesis. In other bloodwood eucalypt species all the primordia in the corolline whorl become continuous at some stage in development, resulting in an operculum that is anatomically unresolvable into its original petaline parts. The varying degrees of this continuity that are evident within individual trees (and even within single flowers) suggests that operculum formation is an epigenetic event that is determined by morphogenetic processes within the flower. It is suggested that these may relate to differing rates of growth in different regions of the bud.     

Ultrastructure of the eye of Urastoma cyprinae (Turbellaria,Alloeocoela)

Summary Urastoma cyprinae (Graff) is a microturbellarian which has been recorded both as a free-living organism by Westblad (1955) and Marcus (1951) and as a commensal in various lamellibranch molluscs (see Burt & Drinnan 1968). The material used in this study came from oysters, Crassostroea virginica, collected off the coast of Prince Edward Island, in which hosts it occurs in large numbers especially during the summer months when the oysters are spawning (Fleming et al. 1981). When U. cyprinae is exposed to light as happens, for example, when an oyster is opened, it shows a marked negative phototactic response.Preliminary work on the fine structure of the photoreceptors in U. cyprinae shows that the two eyes each consists of: (1) a single cup cell full of relatively large, electron-dense pigment granules; (2) a tripartite conical lens system; and (3) what appear to be two photosensitive rhabdomes. The pigment cup cell has a single, well defined nucleus situated basally and close to the membrane of the pigment cell furthest away from the rhabdomeres. The lens system consists of a cone made up of three, separate but equal, parts. Each part has two, flat inner surfaces which join at an angle of 120°, an outer rounded surface, and a rounded upper surface. When these three parts fit together, the cone-shaped lens is formed with the apex of the lens within the cup of the pigment cell and the rounded, convex, broad end of the cone lying more or less at the same level as the top of the pigment cup and below the epidermis layer. The rhabdomeres lie between the electron dense lenses and the inside of the pigment cup. They show connections to the visual cells which are bipolar: one extension joining the rhabdomeres; the other constituting the axon which extends into the centrally situated brain or into the longitudinal, lateral nerves. The axons that enter the brain, form connections with other axons from the other eye. The axons that extend posteriorly in a lateral position, presumably play a role in facilitating the avoidance reaction.The chemical nature of the unusual lens has not yet been determined. This is presently under investigation and will be reported later at which time our work will be discussed in relation to other types of rhabdomeric eyes in the Turbellaria.     

The ultrastructure of the eye of the mosquitofishGambusia affinis

Summary The ultrastructure of the tissue components of the eye ofGambusia affinis, excluding the sensory cells, is described. The cornea consists of two different sections of collagenous layers of different density. The choroid includes an argentea composed of- and-melanophores, lipopterinophores and a choriocapillaris associated with the rete mirabile of the choroid body. Bruch's membrane, underlying the retinal pigment layer, can develop complex associations with fibroblasts delimiting the choriocapillaris. The outer section (stroma) of the iris includes several cell types that are not found in the inner or vitread section. In adultGambusia the lens capsule is well developed, but in twoweek-oldSarotherodon larvae the lens epithelium is covered only by a glycocalyx.     

Keratinization of fish skin with special reference to the catfish Bagarius bagarius

Summary Histochemical reactions indicating keratinization have previously been demonstrated in parts of the epidermis of Bagarius bagarius. Fluorescence histochemistry and electron microscopy have now confirmed these results. Elevated areas of the epidermis are capped by a layer of dead cells with altered contents. On the outer aspect of these cells a dense layer, 18 nm thick, beneath the plasma membrane corresponds to the resistant envelope found in keratinized cells in tetrapod vertebrates. In Bagarius this layer does not extend to all faces of the keratinized cells, but a similar envelope has been detected in two other sites of piscine keratinized epidermis investigated, namely in the breeding tubercles of Phoxinus phoxinus and in the teeth of Lampetra fluviatilis. In the elevated areas of Bagarius-epidermis, the epithelial cells undergo progressive changes in cytoplasmic organization as they become more superficial. The second tier from the surface is sealed by tight junctions and is separated from the overlying keratinized cells by a sub-corneal space resembling that found in keratinized amphibian epidermis. Histochemical evidence of a high lipid content in the outer layers of the epidermis correlates with the presence of lipid inclusions and lamellated membranous profiles in the material studied by electron microscopy. Histochemical results show that the fin skin of Blennius pholis is not keratinized, but secretes a cuticle, histochemically reactive for both proteins and glycoproteins.     

The absolute configuration of the flagellar apparatus in zoospores from two species ofLaminariales (Phaeophyceae

Summary We examined the zoospores produced by the unilocular sporangia ofLaminaria digitata (L.) Lamour. andNereocystis luetkeana Post. & Rupr. by serial sectioning to determine the absolute configuration of their flagellar apparatuses. The basal bodies, which are interconnected by three striated bands, lie parallel to the ventral face of the zoospore, and the posterior basal body always is found to the right of the anterior basal body when the cell is viewed from the ventral face, anterior end up. The four rootlets associated with the basal bodies include a major anterior rootlet of about seven microtubules extending from the anterior basal body along the ventral face towards the apex, a five-membered bypassing rootlet that passes ventral to the basal bodies and is connected to the posterior basal body by a posterior fibrous band, and two short rootlets having a single member each, the minor anterior and posterior rootlets. We consider the configuration observed here to be typical of most phaeophycean motile cells. The flagellar apparatus features suggest a considerable phylogenetic difference between thePhaeophyceae and other classes of chlorophyll c-containing organisms.     

Evidence for hemocyanin formation in the compound eye of Squilla mantis (Crustacea,Stomatopoda)

Summary In the retina and in the subretinal space of the compound eye of Squilla mantis a special kind of pigment cell is present. The crystalline inclusions of this cell have been identified as hemocyanin, as determined (i) by the dimensional congruence of the crystalline substructure with the dimensions of isolated, purified hemocyanin, and (ii) by the immunofluorescence reaction using anti-hemicyanin antibodies. The ultrastructure of these cells, their location and the presence of crystalline bodies in their cytoplasm suggest that they are sites of hemocyanin synthesis and homologous to the cyanocytes or cyanoblasts of Limulus.Supported by grant No. 3,012-0.76 of the Swiss National Science Foundation     

Zoospore ultrastructure in species ofTrebouxia andPseudotrebouxia (Chlorophyta)

Zoospore ultrastructure (incl. flagellar apparatus) has been investigated in three species ofTrebouxia (T. glomerata, T. erici, T. pyriformis) and one species ofPseudotrebouxia (P. impressa) using an absolute configuration analysis. Zoospores in all taxa studied are nearly identical in ultrastructure and exhibit a very distinctive disposition of cell organelles: cells are naked, biflagellate and considerably flattened along the plane of flagellar beat, the single contractile vacuole is located anteriorly in the ventral region of the cell, the nucleus is anteriorly to centrally located in the dorsal region of the cell. A single dictyosome is located close to the anterior, ventral edge of the nucleus. The chloroplast occupies a posterior position in the cell and usually has an anterior profile in the left region of the cell. There are two branched mitochondria per cell or a single mitochondrial reticulum with profiles anterior to the nucleus (in the dorsal region of the cell), and posterior to the nucleus. In zoospores ofTrebouxia spp. the posterior mitochondrial profile is associated with a microbody, inP. impressa zoospores the anterior mitochondrial profiles are associated with a microbody. The zoospores contain a distinctive system of three ER-cisternae: one system links to both basal bodies and extends to the nucleus, the other two systems subtend the plasmamembrane on the left and right broad cell surfaces and extend to the posterior region of the cell. The flagellar apparatus is structurally identical to that previously described for zoospores ofFriedmannia israelensis and exhibits basal body displacement by one basal body diameter into the 11/5 o'clock direction, a non-striated distal connecting fiber, a cruciate microtubular root system lacking system I fibers and presence of a single system II fiber which connects the basal bodies with the nucleus and runs parallel to one of the ER-strands. The left flagellar roots (X-roots) are subtended by a complex set of amorphous and striated material that connects each left root with both basal bodies.—This study demonstrates the close systematic relationship between the phycobiontsTrebouxia andPseudotrebouxia and the generaFriedmannia, Pleurastrum, andMicrothamnion and supports recent classification schemes which place all these taxa into a single order separate from otherChlorophyta. Dedicated to Prof. DrElisabeth Tschermak-Woess on the occasion of her 70th birthday.     

The fine structure of the brain of Gastrocotyle trachuri (Monogenea: Platyhebninthes)

Summary The fine structure of the brain of the monogenean Gastrocotyle trachuri (Platyhelminthes) is described. The brain consists of a central neuropile surrounded by a layer of cell bodies. The neuropile is composed of a fine meshwork of naked neurites which contain various types of vesicles and other organelles although microtubules have not been found. Five kinds of vesicles; three clear types and two dense types, were found within the neuropile.Two types of neuronal cell body were identified on the basis of their vesicle contents although it is possible that these two types represent the extremes of a single cell type. A characteristic feature of the neuronal perikarya of Gastrocotyle is the presence of deep infoldings into the cell of the outer membrane. These infoldings often contain fibrous interstitial material and in a number of cases hemidesmosome-like structures have been found in the distended, distal end of the infoldings.     

Eusynaptomyces benjaminii,spec. nova, (Ascomycetes,Laboulbeniales) und seine Anpassungen an das Fortpflanzungsverhalten seines WirtesEnochrus testaceus (Coleoptera,Hydrophilidae)

Eusynaptomyces benjaminii is described as a new species of the ectoparasiticLaboulbeniales (Ascomycetes). It exists only on two very restricted areas of the body (= position specifity) of its hostEnochrus testaceus (F.) (Coleoptera, Hydrophilidae): on the claws of the right fore-leg and on the lower side of the frontal border of the pronotum. In these two habitatsEu. benjaminii develops two extremely different growth-forms. Male and female hosts are parasitized on somewhat different parts of their body. This can be explained by their mating behaviour. The growth-forms ofEu. benjaminii are so different that one ignorant of the biology of hosts and parasites, might regard them as members of different species or even genera. They are to be interpreted as adaptations of one species to growth positions and mating behaviour of the host. There is no sex-of-host specifity as assumed by certain authors for several species of theLaboulbeniales.

     

Structural changes in spinal ganglion neurons of lizards after cold-exposure

We studied structural changes in spinal ganglion neurons that occur in lizards exposed to the cold, both at the light and electron microscope levels. Two types of perikaryal changes were found in the cold-exposed animals: (a) In 25% of all ganglion neurons, the central region of the perikaryon was devoid of Nissl bodies and a narrow peripheral zone stained deeply basophilic. Electron microscopic examination of these cells showed that mitochondria, Golgi complexes and other organelles were assembled in the central region of the perikaryon, while most cisternae of granular endoplasmic reticulum and free polysomes were confined to the periphery of the perikaryon. These changes seem to take place mainly in dark neurons. (b) In 8.6% of all ganglion neurons, Nissl bodies were present throughout the perikaryon, but separated by large, clear spaces. Under the electron microscope, these clear spaces were filled with large numbers of densely packed filaments. It seems that mainly light neurons undergo this type of structural change. The degree of nuclear eccentricity was significantly greater in the neurons of cold-exposed animals than in controls. The nucleolar volume was significantly increased and both the percentages of nuclei with two nucleoli and of nuclei with 'vacuolated' nucleoli were significantly greater in neurons displaying structural changes than in the other neurons. The structural modifications observed in spinal ganglion neurons of cold-exposed lizards closely resemble those seen in the same lizard neurons following axonal section. They could be due to a) metabolic changes induced by low temperature and fasting, b) alterations in the flow of nerve impulses from the periphery, or c) impaired retrograde transport of trophic substances from the periphery to the cell body.