INFLUENCE OF THE MULTILAYERED STRUCTURE ON THE MORPHOGENESIS OF MARCHANTIA SPERMATIDS

The multilayered structure (MLS) in a spermatid of Marchantia is the morphogenetic blueprint of the headpiece in a mature sperm. As the nucleus begins elongation, a curved, tapered nuclear projection follows the path of microtubules extending from the MLS and becomes inserted into an indented zone at the rear of the asymmetric organelle. The indented zone defines the most forward penetration of the nucleus into the sperm headpiece. Partial disorganization of MLS lower strata nearest the nuclear projection facilitates overlapping of the nucleus with the rearward part of the anterior mitochondrion. At the front of the nascent headpiece, the mitochondrion is stabilized against microtubules following total disorganization of intervening MLS strata. Penetration of the nuclear projection along the MLS and directed disorganization of MLS lower strata control ultimate disposition of headpiece components. The headpiece is isolated and molded into final shape by undercutting and constriction of the cell membrane.     

Ultrastructure of the spermatozoid of Lycopodium obscurum (Lycopodiaceae)

Ultrastructural observations reveal that the spermatozoid of Lycopodium obscurum is crescent shaped and contains two posteriorly directed flagella that are inserted at the front of the cell. The nucleus is broad and elongated with a narrow posterior projection or nuclear diverticulum. Spline microtubules (MTs) number 180 at their maximum and provide the framework for the cell. These MTs extend from the anterior of the locomotory apparatus and along the outermost surface of the nucleus, with a central shank of 14–17 MTs encircling the cell for at least one-third gyre beyond the nucleus. The two basal bodies are slightly staggered and positioned at the front of the cell over a highly elongated multilayered structure (MLS). The MLS extends laterally around the cell anterior and curves posteriorly over the nucleus. One large anterior mitochondrion is situated subjacent to the MLS, while numerous small mitochondria are scattered near or among the lobes of the single plastid. The plastid rests on the inner nuclear surface and contains numerous large starch grains. This cell differs from that of L. cernuum, the only other species of Lycopodium examined to date, in that it is more elongated and has an anterior-posterior orientation of the nucleus, basal bodies, MLS, and spline. Comparisons with coiled gametes of bryophytes and Selaginella suggest that some degree of coiling and cell streamlining may be ancestral in archegoniate spermatozoids.     

Ultrastructural studies of spermatogenesis inAnthocerotophyta V. Nuclear metamorphosis and the posterior mitochondrion ofNotothylas orbicularis andPhaeoceros laevis

Summary Ultrastructural observations reveal that the spermatozoids of the hornwortsNotothylas andPhaeoceros contain two mitochondria and not one as described previously. Mitochondrial ontogeny and nuclear metamorphosis during spermiogenesis in these plants differ from all other archegoniates. The discovery that the posterior region of the coiled nucleus (when viewed from the anterior aspect) lies to the left of the anterior, in striking contrast to the dextral coiling of the nucleus of spermatozoids of other embryophytes, underlines the isolated nature of the hornworts among land plants. As the blepharoplast develops, the numerous ovoid mitochondria initially present in the nascent spermatid fuse to form a single elongated organelle which is positioned subjacent to the MLS and extends down between the nucleus and plastid. At the onset of nuclear metamorphosis, the solitary mitochondrion has separated into a larger anterior mitochondrion (AM) associated with the MLS and a much smaller posterior mitochondrion (PM) adjacent to the plastid. The PM retains its association with the plastid and both organelles migrate around the periphery of the cell as the spline MTs elongate. By contrast, in moss spermatids, where mitochondria undergo similar fusion and division, the AM is approximately the same size as the PM and the latter is never associated with the spline. As in other archegoniates, except mosses, spline elongation precedes nuclear metamorphosis in hornworts. Irregular strands of condensed chromatin compact basipetally to produce an elongated cylindrical nucleus which is narrower in its mid-region. During this process excess nucleoplasm moves rearward. It eventually overarches the inner surface of the plastid and entirely covers the PM.Abbreviations ABB anterior basal body - AM anterior mitochondrion - LS lamellar strip - MLS multilayered structure - MT microtubule - PBB posterior basal body - PM posterior mitochondrion     

The cytology and ultrastructure of zoospores of Hydrurus foetidus (Chrysophyceae)

The unusual tetrahedral shape of Hydrurus foetidus (Vill.) Trev. zoospores is associated with a complex skeletal system of microtubules extending from a broad flagellar root (up to 19 microtubules) into each of three, pointed anterior processes. The posterior end, also pointed and supported by a separate set of microtubules, contains a single large chloroplast with a prominent posterior furrow containing mitochondrial elements. A large immersed pyrenoid is penetrated by paired thylakoids. There is no eyespot. Numerous large Golgi bodies occur immediately anterior to the nucleus and up to 5–6 contractile vacuoles lie near the cell surface at the anterior end. Two terminally inserted flagella extend from the cell surface, a long one serving for cell locomotion, and the other vestigial with an axonemal pattern of 9+0. The flagellar root system consists of: (1) a thin, striated rhizoplast extending from the basal body of the long flagellum and ramifying over the surface of a conspicuous, anteriorly directed, conical projection of the nucleus; (2) a broad microtubular root which emanates from near the basal body of the long flagellum and appears to function as a MTOC; (3) a compound root, consisting of a striated fiber and two associated microtubules, which runs alongside the basal body of the stubby flagellum before terminating at the cell surface; and (4) a short two-membered microtubular root, also associated with the basal body of the stubby flagellum. Other components of the flagellar apparatus include a large dense body near the proximal end of the basal body of the short flagellum, and a small, dense, core-like structure closely associated with one of its triplet fibers. The flagellar apparatus of H. foetidus is remarkably similar in ultrastructure to that of Chrysonebula holmesii Lund.     

The fine structure of spermiogenesis in the Amblypygi and the Uropygi (Arachnida)

Summary Spermiogenesis in one species from each of the arachnid groups Amblypygi and Uropygi is described by electron microscopy: The whip spider,Tarantula marginemaculata (Amblypygi), and the whip-scorpion,Mastigoproctus giganteus, (Uropygi). In both species the earliest spermatid has a spherical nucleus and soon acquires an anterior acrosome and a posterior flagellar tail. The flagellun is peculiar in having a 9 + 3 axonemal pattern. By the mid-spermatid stage, the nucleus becomes conspicuously elongated, possibly through the agency of a manchette of microtubules. In the late spermatid, the elongated nucleus begins to coil posteriorly; simultaneously the middle piece and the tail flagellum begin to retract into the cell body to form a coiled intracellular axonema. Membranous profiles appear in the peripheral cytoplasm, possibly to accommodate a decrease in the total area of plasma membrane. The mature sperm is a spherical cell, which includes the following organelles in twisted and fully coiled configuration: an elongated nucleus, an acrosome and an acrosomal filament, a long middle piece with helically arranged mitochondria and an intracellular axonema.     

Ultrastructural studies of mutant spermatozoids in ferns. I. The mature nonmotile spermatozoid of mutation 230X in Ceratopteris thalictroides(L.)Brongn

Electron microscopy reveals that nonmotility in the spermatozoids of mutant 230X of the fern Ceratopteris thalictroides results from highly aberrant flagella. With respect to its mitochondrial complement, amyloplasts, condensed chromatin within the nucleus and the multilayered structure (MLS), the mutation is almost indistinguishable from the wild-type spermatozoids. In contrast to flagellar mutations in other organisms (man, mouse, Drosophila, Chlamydomonas), which principally affect the microtubules of the axoneme, the basal body cartwheel is lacking in 230X. In its absence, compound microtubules with shared walls are still present, but in highly disorganized arrays. Since the amount of polymerized tubulin in the spermatozoids of 230X is approximately the same as in the wild type, the mutation does not seem to affect microtubule synthesis or assembly. Centriolar cartwheels appear to be essential templates for the alignment of triplet and doublet tubules in regular radial arrays. The MLS in 230X is almost normal, whereas the flagella are aberrant, indicating that there are two distinct functional classes of microtubules in archegoniate spermatozoids. In contrast to the helix of 3½ gyres found in the wild type, nuclear morphology in 230X exhibits profound distortions ranging from deep channels and holes to supernumerary attenuated arms. Parts of nuclei associated with the MLS are almost normal, but malformations are in variably associated with the presence of microtubules of the aberrant flagella that are in close proximity t o the nuclear surface. The shapes of the teratologies are directly related to the number and configuration of the adjacent perinuclear tubules. From these findings, it is argued that microtubules have a crucial role in nuclear shaping in archegoniates; and that the precise form of the nucleus is closely related to the geometry and development of the MLS. On the other hand, it is difficult to envisage how microtubules growing in the chaotic arrays found in 230X could themselves generate shaping forces, More likely, the actual force-generating system, situated in or near the nuclear envelope, has become misaligned and severely restricted by the perinuclear arrays of flagellar tubules, which function as cytoskeletal elements additional to those of the normal MLS. Archegoniate plants are particularly advantageous for the detection of basal body mutants, since centrioles are absent from the mitotic apparatus. Cytological and hybridization studies of 230X affirm the nuclear basis of the mutation, and provide no support for the possible genetic autonomy of centrioles.     

COMPARATIVE ULTRASTRUCTURAL STUDIES OF SPERMATOGENESIS IN THE METZGERIALES (HEPATOPHYTA) II. THE BLEPHAROPLAST OF BLASIA PUSILLA

As in other hepatics, the young spermatid of Blasia pusilla contains a well-developed blepharoplast comprising a four-layered multilayered structure (MLS) and two overlying dimorphic basal bodies. The asymmetrical spline (S₁ or upper stratum of the MLS) numbers 20 or 21 microtubules (MTs) at its anterior tip and reduces to eight at the posterior limit of the lamellar strip (LS). Behind this the shank of the spline is five or six tubules in width over most of its length, approximately one revolution of the circumference of the gamete. The three-microtubule spline aperture underlies the anterior basal body and like those of most hepatics, it is closed at its anterior end. The asymmetrical LS (approx. 2.0 μm in length) is characterized by a right-hand posterior notch which lies below the spline aperture at the region of the cartwheel configuration of the anterior basal body (ABB). The staggered dimorphic basal bodies overlap for approximately one third of their lengths. Both lie parallel to the long axis of the spline. As in other hepatics, the ABB (1.2 μm in length) is subapical and comprises an anterior hub extension with progressive rearward additions of lateral, dorsal and ventral triplets. Over most of its length (2.1 μm) the longer posterior basal body (PBB) consists of a distinct central hub and three ventral triplets. Transition zones of both basal bodies contain stellate configurations into which the two central axonemal MTs frequently extend. The blepharoplast of Blasia shows several features in common with leafy, simple thalloid and complex thalloid liverworts. Compared with the few Metzgeriales observed thus far, the LS is less elongate and the basal bodies less staggered. Dimensions of basal body components and spline dimensions, however, are comparable to those of most leafy and thalloid hepatics. Striking similarities with the complex thalloid liverworts include a posterior notch in the LS and a spline aperture three MTs wide.     

SPERMATOGENESIS IN LYCOPODIUM: THE MATURE SPERMATOZOID

The mature spermatozoid of Lycopodium cernuum is a blunt ended, fusiform cell, 8–10 μm long by 4–5 μm wide. A multilayered structure (MLS) and a subtending anterior mitochondrion are located at the anterior of the cell. The MLS is coiled through 1–1.5 gyres in a shallow sinistral helix around the periphery of the cell. The MLS would be triangular in outline if unwound and laid flat, about 1.4 μm wide, 7.5–8 μm long, and 80 nm thick. The MLS comprises four layers, S₁–S₄. The S₁ forms the spline, a supportive sheet of microtubules; the S₂, lamellate in younger stages, is an homogeneous, darkly staining layer in the mature sperm; the S₃ and S₄ retain their lamellate appearance and are delimited by lateral connections. Approximately 200 S₁ microtubules extend posteriorly from the MLS at about 45° to the MLS long axis and form a partial sheath around the nucleus. The two basal bodies are located on opposite sides of the cell external to the MLS. Each is tangential to the curve of the MLS and surrounded by a globular matrix. At their attachment, the axonemes are oriented laterally and are antiparallel to each other. Distally, the flagella, each about 38 μm long, trail behind the cell as it swims. The nucleus is roughly ovoid, about 4 μm diam, and centrally or sometimes laterally located. The greater volume of the nucleus is occupied by condensed, amorphic chromatin. Cavities within the chromatin are often seen to contain spheroidal inclusions that have two differently staining regions. The inclusions are also located at the periphery of the chromatin. The posterior of the cell is occupied by several small mitochondria and an amyloplast, about 2 μm diam containing numerous starch grains.     

FINE STRUCTURE OF ZOOSPOROGENESIS, ZOOSPORE GERMINATION, AND EARLY GAMETOPHYTE DEVELOPMENT IN CLADOPHORA SURERA (CLADOPHORALES, CHLOROPHYTA)

The fine structure of zoosporogenesis, zoospore germination, and early gametophyte development in Cladophora surera Parodi et Cáceres were studied. Zoosporogenesis started with simultaneous meiosis in all nuclei of apical initial cells. The resulting haploid nuclei duplicated in turn by successive centric, closed mitoses. Then, each initial cell divided into two short zoosporangia. Numerous vacuoles appeared around each sporic nucleus. The delimitation of uninucleate zoosporocytes occurred by cytokinetic furrows produced by the coalescence of tiny, clear vesicles, without microtubules. Final shape of the zoospore resulted from gradual expulsion of vacuoles from the cell body. Mature biflagellate zoospores exhibited a conspicuous apical papilla containing fine granular globules, the basal apparatus, and a microtubular "umbrella" formed by numerous cortical microtubules that ran backward the length of the cell body. The chloroplast showed a conspicuous eyespot. The zoosporangial wall disorganized at the pore through which the zoospores were liberated. Zoospores settled on a substrate by their anterior papilla secreting an adhesive. Germination involved retraction of the apical papilla, loss of the "umbrella" microtubules and eyespot, and the lateral absorption of the entire flagellar apparatus, i.e. basal apparatus plus axoneme, into the cytoplasm. Early gametophyte development involved the synthesis of a thin, young cell wall, the development of outer peripheral vacuoles, the appearance of the marginal reticulate chloroplast, and the formation of the first central vacuoles derived from abundant endoplasmic reticulum. Close to the plasmalemma ran longitudinally oriented cortical microtubules. Eventually, the germling developed an achlorophylic, elongated rhizoidal portion.     

ULTRASTRUCTURE OF CEPHALEUROS VIRESCENS (CHROOLEPIDACEAE; CHLOROPHYTA). IV. ABSOLUTE CONFIGURATION ANALYSIS OF THE CRUCIATE FLAGELLAR APPARATUS AND MULTILAYERED STRUCTURES IN THE PRE- AND POST-RELEASE GAMETES

Transmission electron microscopy of pre-release and post-release biflagellate gametes of Cephaleuros virescens has produced comparative data on these cells and on the detailed absolute arrangement of the flagellar apparatus. In all major respects including the presence of two multilayered structures (MLS's) the closely compacted, non-motile but mature pre-release gametes are similar to the mature, free swimming post-release gametes. The elongated shape of the free-swimming gametes differs from the more compact form of the pre-release gametes, but does not reflect a major difference in the arrangement of internal components. The flagella are bilaterally keeled and each keel contains a cylindrical element. Each flagellar base is encircled by a densely staining collar of modified plasmalemma at the point of entry into the apical papilla. The equal anterior flagella enter the papilla from opposite sides; their basal bodies are parallel and overlapping. Each terminates in a densely staining terminal cap. No capping plate is present. Each basal body is associated both with a three-layered MLS, the anterior layer of which becomes a lateral microtubular spline of 2 to 8 microtubules, and with an additional medial compound root of two layers of microtubules (2 over 4 or 5). Both the compound microtubule root and the spline may acquire additional microtubules as they extend distally in close proximity to mitochondria and the plasmalemma. No striated roots, or rhizoplasts, have been observed. Two densely staining plaques are associated with the plasma membrane at specific anterior sites and may be comparable to the presumptive mating structures seen in other green algal motile cells. The reversed bilateral symmetry of the cells produces two possible arrangements of the flagellar apparatus, namely, a 11/5 (or left-handed) arrangement or a 1/7 (or right-handed) arrangement. Only 11/5 cells have been found. Despite the presence of distinct multilayered structures, some aspects of the gametes of Cephaleuros quite closely resemble the cruciate motile cells of algae now regarded by some authors as typical of Ulvophyceae, sensu Stewart and Mattox.     

ULTRASTRUCTURAL STUDIES OF SPERMATOGENESIS IN THE ANTHOCEROTALES. I. THE BLEPHAROPLAST AND ANTERIOR MITOCHONDRION IN PHAEOCEROS LAEVIS: EARLY DEVELOPMENT

Electron microscopic examination of thin sections showed that the blepharoplast of a young spermatid of Phaeoceros consists of two side-by-side centrioles and an accumulation of osmiophilic, granular matrix at their proximal ends. Lying between these nearly parallel organelles is a dark-staining body that will later disappear at the onset of flagellogenesis. For a brief period the centrioles are oriented perpendicular to the nuclear surface so that the granular matrix at their proximal ends is confluent with the nuclear envelope; furthermore, the nucleoplasm immediately in front of the centrioles becomes densely staining. The multilayered structure (MLS) develops directly under the centrioles. It comprises a band of 12 microtubules (the S₁ stratum) and three lower strata (S_2–4) whose constitutent lamellae are oriented at an oblique angle to the S₁ axis. While the S₁ tubules grow rearward over the nucleus which forms a beak adjacent to the posterior end of the lamellar strata, the centrioles are transformed into basal bodies with the distal growth of the axonemes and the proximal growth of the central cartwheels and lowermost triplets. The proximal ends of the basal bodies and the S₁ tubules overlying the lamellar strata are invested with osmiophilic matrix that extends down to the S₂ layer and may temporarily occlude the lamellar plates. At the onset of nuclear elongation an anterior mitochondrion becomes situated close beneath the lamellar strata which extend laterally beyond the S₁ tubules.     

Ultrastructure of the Spermatozoon of Avitellina centripunctata(Cestoda,Cyclophyllidea), a Parasite of the Small Intestine of Cattle in Senegal

The Avitellina centripunctataspermatozoon is filiform, tapered at both ends and lacks mitochondria. The anterior extremity exhibits an apical cone and a crested–like body 150–200 nm thick. The axoneme is surrounded by a fine layer of lucent cytoplasm and a sheath of electron–dense material. The cytoplasm is slightly electron–dense at the anterior tip of the apical cone and in region IV of the spermatozoon. Over the rest of the gamete it is subdivided into numerous electron–lucent compartments by irregularly spaced walls. The nucleus is electron–dense. It interposes itself between the cortical microtubules which are all electron–dense centred and spiralized along their whole length. An apical zone containing spiralized microtubules, cortical microtubules which are all electron–dense centred and stop before reaching the posterior extremity of the nucleus, as well as the subdivision into cavities by intracytoplasmic proteinaceous material, have never been described before in a cestod. Moreover, the crested–like body of Avitellina centripunctatais the thickest of those which have been described to date in the cestods.     

Microtubule-driven nuclear movements and linear elements as meiosis-specific characteristics of the fission yeasts Schizosaccharomyces versatilis and Schizosaccharomyces pombe

Meiotic prophase in Schizosaccharomyces pombe is characterized by striking nuclear movements and the formation of linear elements along chromosomes instead of tripartite synaptonemal complexes. We analysed the organization of nuclei and microtubules in cells of fission yeasts undergoing sexual differentiation. S. japonicus var. versatilis and S. pombe cells were studied in parallel, taking advantage of the better cytology in S. versatilis. During conjugation, microtubules were directed towards the mating projection. These microtubules seem to lead the haploid nuclei together in the zygote by interaction with the spindle pole bodies at the nuclear periphery. After karyogamy, arrays of microtubules emanating from the spindle pole body of the diploid nucleus extended to both cell poles. The same differentiated microtubule configuration was elaborated upon induction of azygotic meiosis in S. pombe. The cyclic movements of the elongated nuclei between the cell poles is reflected by a dynamic and coordinated shortening and lengthening of the two microtubule arrays. When the nucleus was at a cell end, one array was short while the other bridged the whole cell length. Experiments with inhibitors showed that microtubules are required for karyogamy and for the elongated shape and movement of nuclei during meiotic prophase. In both fission yeasts the SPBs and nucleoli are at the leading ends of the moving nuclei. Astral and cytoplasmic microtubules were also prominent during meiotic divisions and sporulation. We further show that in S. versatilis the linear elements formed during meiotic prophase are similar to those in S. pombe. Tripartite synaptonemal complexes were never detected. Taken together, these findings suggest that S. pombe and S. versatilis share basic characteristics in the organization of microtubules and the structure and behaviour of nuclei during their meiotic cell cycle. The prominent differentiations of microtubules and nuclei may be involved in the pairing, recombination, and segregation of meiotic chromosomes.     

The flagellar apparatus of the golden algaSynura uvella: Four absolute orientations

Summary Flagellated vegetative cells of the colonial golden algaSynura uvella Ehr, were examined using serial sections. The two flagella are nearly parallel as they emerge from a flagellar pit near the apex of the cell. The photoreceptor is restricted to swellings on the flagella in the region where they pass through the apical pore in the scale case and the swellings are not associated with the cell membrane or an eyespot. A unique ring-like structure surrounds the axonemes of both flagella at a level just above the transitional helix. The basal bodies are interconnected by three striated, fibrous bands. Four short (<100 nm) microtubules lie between the basal bodies at their proximal ends. Two rhizoplasts extend down from the basal bodies and separate into numerous fine striated bands which lie over the nucleus. Three- and four-membered microtubular roots arise from the rhizoplasts and extend apically together. As the roots reach the cell anterior, the three-membered root bends and curves clockwise to form a large loop around the flagella; the four-membered root bends anticlockwise and terminates under the distal end of the three-membered root as it completes the loop. There are four absolute orientations, termed Types 1–4, in which the flagellar apparatus can occur. With each orientation type the positions of the Golgi body, nucleus, rhizoplasts, chloroplasts and microtubular roots change with respect to the flagella, basal bodies and photoreceptor. Two new basal bodies appear in pre-division cells, and three short microtubules appear in a dense substance adjacent to each new basal body. Based upon the positions of new pre-division basal bodies, a hypothesis is proposed to explain why there are four orientations and how they are maintained through successive cell divisions.     

Dynamic changes in microtubule organization during division of the primitive dinoflagellate Oxyrrhis marina

The marine dinoflagellate Oxyrrhis marina has three major microtubular systems: the flagellar apparatus made of one transverse and one longitudinal flagella and their appendages, cortical microtubules, and intranuclear microtubules. We investigated the dynamic changes of these microtubular systems during cell division by transmission and scanning electron microscopy, and confocal fluorescent laser microscopy. During prophase, basal bodies, both flagella and their appendages were duplicated. In the round nucleus situated in the cell centre, intranuclear microtubules appeared radiating toward the centre of the nucleus from densities located in some nuclear pores. During metaphase, both daughter flagellar apparatus separated and moved apart along the main cell axis. Microtubules of ventral cortex were also duplicated and moved with the flagellar apparatus. The nucleus flattened in the longitudinal direction and became discoid-shaped close to the equatorial plane. Many bundles of microtubules ran parallel to the short axis of the nucleus (cell long axis), between which chromosomes were arranged in the same direction. During ana-telophase, the nucleus elongated along the longitudinal axis and took a dumbbell shape. At this stage a contractile ring containing actin was clearly observed in the equatorial cortex. The cortical microtubule network seemed to be cut into two halves at the position of the actin bundle. Shortly after, the nucleus divided into two nuclei, then the cell body was constricted at its equator and divided into one anterior and one posterior halves which were soon rebuilt to produce two cells with two full sets of cortical microtubules. From our observations, several mechanisms for the duplication of the microtubule networks during mitosis in O. marina are discussed.     

Spermiogenesis and spermatozoon ultrastructure of the dilepidid cestode Molluscotaenia crassiscolex (von Linstow, 1890), an intestinal parasite of the common shrew Sorex araneus

Marigo, A.M., Bâ, C.T. and Miquel, J. 2011. Spermiogenesis and spermatozoon ultrastructure of the dilepidid cestode Molluscotaenia crassiscolex (von Linstow, 1890), an intestinal parasite of the common shrew Sorex araneus. —Acta Zoologica (Stockholm) 92 : 116–125. Spermiogenesis in Molluscotaenia crassiscolex begins with the formation of a differentiation zone containing two centrioles. One of the centrioles develops a flagellum directly into the cytoplasmic extension. The nucleus elongates and later migrates along the spermatid body. During advanced stages of spermiogenesis, a periaxonemal sheath appears in the spermatid. Spermiogenesis finishes with the appearance of a single helicoidal crested body at the base of the spermatid and, finally, the narrowing of the ring of arched membranes causes the detachment of the fully formed spermatozoon. The mature spermatozoon of M. crassiscolex exhibits a partially detached crested body in the anterior region of the spermatozoon, one axoneme, twisted cortical microtubules, a periaxonemal sheath, and a spiralled nucleus. The anterior spermatozoon extremity is characterized by the presence of an electron‐dense apical cone and a single spiralled crested body, which is attached to the sperm cell in the anterior and posterior areas of region I, whereas in the middle area it is partially detached from the cell. This crested body is described for the first time in cestodes. The posterior extremity of the male gamete exhibits only the disorganizing axoneme. Results are discussed and compared particularly with the available ultrastructural data on dilepidids sensu lato.     

The Spermatozoon of Brachionus plicatilis(Rotifera,Monogononta) With Some Notes on Sperm Ultrastructure in Rotifera

The spermatozoon of B. plicatilisis a thread–like cell with an anterior flagellar portion and a posterior cell body. The flagellum has a lateral ‘undulating membrane’, containing a folded longitudinal cisterna and an axoneme. The basal body of the axoneme is at the anterior tip. The axoneme lacks outer dynein arms and extends through the entire flagellar region and most of the cell body. The main portion of the flagellum and of the cell body contains a series of vesicles with tightly packed tubules that may serve as a cytoskeleton. The cell body contains a partly condensed nucleus, several mitochondria and some cytoplasm. Some elongated mitochondria are arranged in the postnuclear region. When the spermatozoon moves, the undulations propagate from the basal body at the flagellar tip. Late spermatids can be recognized by the nucleus and the flagellum being coiled and enclosed within a common cell membrane. As in other rotifers, there are cigar–like cell products (‘rods’) in the testes. The general organization of the cell, including the absence of an evident acrosome, resembles that of the other known monogonont sperm types.     

STUDIES OF SPERMATOGENESIS IN THE HEPATICAE V. BLEPHAROPLAST DEVELOPMENT IN MARCHANTIA POLYMORPHA

Coaxial centrioles and a microtubule organizing center (MTOC) constitute each centrosome in spermatid mother cells of Marchantia polymorpha. During cell division the centrosome separates at its midregion and the two centrioles undergo a planar rotation that brings them to lie somewhat staggered and nearly parallel with their proximal ends embedded in osmiophilic granular material similar in appearance to that of the MTOC. Microtubules of the multilayered structure (MLS) arise in this material below the posterior centriole and parallel to its long axis. The rotation of centrioles and the initiation of S₁ tubules below the posterior centriole determine polarity of the incipient blepharoplast. Lower MLS strata are formed under the anterior centriole by the compaction of granular, osmiophilic matrix. Formation and growth of S₂ vertical lamellae occur at the left front edge of the MLS in association with MTOC-like matrix localized near the cell membrane. The MLS enlarges to about 0.4 μm wide by 0.6 μm long and is ovoid in outline except for a short distal projection underlying the posterior centriole. Subsequently the lamellae are transformed into homogenous, osmiophilic matrix that contributes directly to the expansion of all MLS strata including microtubules. The stratum of lamellae is interpreted as a planar MTOC subject to morphogenetic control. Each of the four strata grows proximally while the tapering distal projection lengthens beneath the posterior basal body. Dense matrix above the MLS, apparently elaborated by the S₂ layer, is organized into cartwheel and triplet components of the basal bodies’ proximal extensions. Organization of triplet tubules proceeds from proximal to distal toward preexisting triplets. Osmiophilic matrix contributes to the formation of microtubule keels and osmiophilic crests and may serve as a cementing material that stabilizes the spatial relationships of blepharoplast components. After full expansion of the MLS’ lower strata, the S₂ layer is reorganized into lamellae. Flagellar growth in Marchantia is postulated to involve a process whereby subunits or their precursors are elaborated by the MLS, translocated to the distal end of the flagellum and incorporated into the axonemal tubules. When MLS microtubules elongate to form a long, narrow band, the distal half of the S₂ layer is again in the osmiophilic matrix state.     

Behaviors of nucleus, basal bodies and microtubules during eupyrene and apyrene spermiogenesis in the silkworm, Bombyx mori (Lepidoptera)

Observations with immunostaining for tubulin and electron microscopy revealed that silkworm eupyrene spermiogenesis was characterized by an attachment of the basal body to the nucleus except in the period of movement for unidirectional arrangement. In young eupyrene sperm, a microtubule basket caught the nucleus, which thereafter was transformed elliptically. Microtubules were also observed along the elongated acrosome and mitochondrial derivatives. During apyrene spermiogenesis, however, the basal body was not attached to the nucleus and approached the head cyst cell after the completion of unidirectional arrangement, leaving the round nucleus in the middle of the cell. The presence or absence of the phenomenon in which the basal body attaches to the nucleus seems to be essential in the course of diverse spermatogenesis of the silkworm.     

Fine structure of the giant aflagellate spermatozoon in pseudostomum quadrioculatum (leuckart) (platyhelminthes,prolecithophora)

The giant aflagellate spermatozoa of P. quadrioculatum are composed of two different parts: a thicker head piece and a more slender tail piece. In the head there exist a large elongated nucleus and an elongated mitochondrial derivative situated in a groove-like cavity of the nucleus. In mature spermatozoa the nuclear material is arranged in many small membrane bounded areas. Both structures, nucleus and mitochondrial derivative, are spirally coiled. The outer part of the membrane in the mitochondrial derivative forms many loop-like foldings. Both organelles continue to the tail in form of two small, helically coiled ribbons; the nucleus is anchored within the mitochondrial derivative by an electron-opaque process. A sheath of spirally-orientated cortical microtubules starting from the tip of the head runs to the tip of the tail under the cell membrane. In addition, a second sheath of tubules occurs in the tail region, these tubules also run parallel to each other, but in the opposite direction to the microtubules of the outer sheath.The possible relations between the structures observed and the motility of the spermatozoa are discussed; in addition, some phylogenetic comments are attempted.Abbreviations c — cerebrum - com — cortical microtubules - cop — copulatory organ - fm — foldings of the mitochondrial membrane - l — lattice - mid — mitochondrial derivative - mt — microtubules - n — nucleus - ne — nuclear envelope - ph — pharynx - pn — protonephidium - rp — ribbon-like nuclear process - te — testis - tt — testis - tt — tip of the tail - vi — vitellarium - vs — vesicula seminalis