The cytoskeletal involvement in cellularization of theDrosophila melanogaster embryo

Summary The distribution and arrangement of cytoskeletal components in the early embryo ofDrosophila melanogaster were examined by thin-section electron microscopy to elucidate their involvement in the formation of the cellular blastoderm, a process called cellularization. During the final nuclear division in the cortex of the syncytial blastoderm bundles of astral microtubules were closely associated with the surface plasma membrane along the midline where a new gutter was initiated. Thus the new gutter together with the pre-formed ones compartmentalized the embryo surface to reflect underlying individual daughter nuclei. Subsequently such gutters became deeper by further invagination of the plasma membrane between adjacent nuclei to form so-called cleavage furrows. Nuclei simultaneously elongated in the direction perpendicular to the embryo surface and numerous microtubules from the centrosomes ran longitudinally between the nucleus and the cleavage furrow. Microtubules often appeared to be in close association with the nuclear envelope and the cleavage furrow membrane. The plasma membrane at the advancing tip of the furrow was always undercoated with an electron-dense layer, which could be shown to be mainly composed of 5–6 nm microfilaments. These microfilaments were decorated with H-meromyosin to be identified as actin filaments. As cleavage proceeded, each nucleus with its perikaryon became demarcated by the furrow membrane, which then extended laterally to constrict the cytoplasmic connection between each newly forming cell and the central yolk region. The cytoplasmic strand thus formed possessed a prominent circular bundle of microfilaments which were also decorated with H-meromyosin and bidirectionally arranged, similar in structure to the contractile ring in cytokinesis. These observations strongly suggest that both microtubules and actin filaments play a crucial role in cellularization ofDrosophila embryos.     

Distinct lobes of Limulus ventral photoreceptors. II. Structure and ultrastructure

The structure of Limulus ventral photoreceptors fixed in situ has been investigated using light and electron microscopy and computer-assisted reconstruction and planimetry. Photoreceptors occur singly and in clusters. All photoreceptors have two types of lobes. The rhabdomeral lobe (R lobe) appears to be specialized for light sensitivity, containing the rhabdomere, which completely covers its external surface and forms infoldings into the lobe. The structure of the external rhabdom differs from that within infoldings. The other main structures of the R lobe are the palisades along the rhabdom, multivesicular bodies, lamellar bodies, and mitochondria. The arhabdomeral lobe (A lobe) bears the axon and contains the nucleus, clusters of residual bodies, lamellar arrays of endoplasmic reticulum, masses of glycogen, lipid droplets, and Golgi complexes. The R lobe and A lobe are analogous to the outer and inner segments of vertebrae photoreceptors. In single photoreceptors A and R lobes are separated by an indentation filled with glial processes. Computer reconstructions of cell clusters reveal that each cell has both types of lobes and an axon. Most of the rhabdom is formed from abutting arrays of external rhabdom from the R lobes of different members of the cluster. Efferent fibers containing characteristic angular granules penetrate single cells and clusters in glial invaginations. The main, if not exclusive, target of the efferent fibers is the internal rhabdom.     

FINE STRUCTURE OF CALONEIS AMPHISBAENA (BACILLARIOPHYCEAE)1

The structure of the motile pennate diatom Caloneis amphisbaena Cleve is described, with emphasis on the lateral, lobed pyrenoid with neither a limiting membrane nor penetration by thylakoids, an interphase nucleus with centers of condensed chromatin, paired dictyosomes, and mitochondria cradled within the chambers of the valve. Microfilaments forming two bundles which lie beneath each raphe slit are of the same size and appearance as actin microfilaments associated with other motile systems.     

Comparative morphology among trunk limbs of Caenestheriella gifuensis and Leptestheria kawachiensis (Crustacea: Branchiopoda: Spinicaudata)

Morphological differences among groups of the 24 trunk limbs of Caenestheriella gifuensis (Ishikawa, 1895) and differences between males and females are described and illustrated. A setose attenuate lobe located proximally near enditic lobe 1 and a discoid lobe covered with small setae proximal to enditic lobe 1 are newly described. The five ventral enditic lobes, endopod, exopod, and dorsal exite of traditional spinicaudatan morphology are redescribed. Trunk limbs 1–4 of females bear a palp on enditic lobe 5 and trunk limbs 1–15 of males bear a similar palp. A second, articulating palp is associated with the base of the endopod of trunk limbs 1–2 of males. The proximal part of trunk limbs 19–24, bearing enditic lobe 1, articulates by an arthrodial membrane with the remainder of the limb, and the exite is distal to this arthrodial membrane. Development of trunk limbs, ascertained through an examination of early juvenile instars of Leptestheria kawachiensis Uéno, 1927, includes an asetose limb followed in time by a series of setose limbs that increase in morphological complexity with age. The number of lobes on the asetose limb varies from seven (corresponding to five enditic lobes, an endopod, and an exopod) on anterior limbs to five on trunk limb 24, which lacks the lobes corresponding to enditic lobe 4 and the endopod; these two structures are added later to setose limbs. The attenuate lobe, the discoid lobe, the exite of all trunk limbs, and the palps of the anterior trunk limbs are added to the setose limbs. Development of anterior limbs is accelerated relative to that of posterior limbs, and development of the more posterior limbs is truncated relative to that of limbs immediately anterior to them. Enditic lobe 4 and the endopod of limbs like trunk limb 24 develop from, or are patterned by, enditic lobe 5; the articulating palp of male trunk limbs 1–2 also may be added in this way. A comparison of these observations with development of the copepod maxilliped suggests that the spinicaudatan trunk limb is composed of a praecoxa with three lobes, a coxa and a basis each with one lobe, and an endopod of three segments in females and four in males. This is similar to the homology scheme previously proposed by Hansen in 1925. A critique is given of attempts to homologize parts of arthropod limbs based on developmental gene expression patterns. Stenopodal to phyllopodal transformations of maxillipeds in copepods provide a model at least partly applicable to spinicaudatans, and a ‘multibranched’ interpretation of spinicaudatan (and by extension branchiopodan) limb morphology is rejected. There is nothing intrinsic to the structure of the adult trunk limbs suggesting that they are similar to the adult limbs of the ancestral branchiopod or the ancestral crustacean, but early developmental steps of more posterior limbs are good matches for the morphology of an ancestral crustacean biramal limb predicted by a hypothesis of duplication of the proximo‐distal axis. © 2003 The Linnean Society of London, Zoological Journal of the Linnean Society, 2003, 139 , 547–564. No claim to original US government works.     

Structural characterization of the NAP; the major adhesion complex of the human pathogen Mycoplasma genitalium

Mycoplasma genitalium, the causative agent of non‐gonococcal urethritis and pelvic inflammatory disease in humans, is a small eubacterium that lacks a peptidoglycan cell wall. On the surface of its plasma membrane is the major surface adhesion complex, known as NAP that is essential for adhesion and gliding motility of the organism. Here, we have performed cryo‐electron tomography of intact cells and detergent permeabilized M. genitalium cell aggregates, providing sub‐tomogram averages of free and cell‐attached NAPs respectively, revealing a tetrameric complex with two‐fold rotational (C2) symmetry. Each NAP has two pairs of globular lobes (named α and β lobes), arranged as a dimer of heterodimers with each lobe connected by a stalk to the cell membrane. The β lobes are larger than the α lobes by 20%. Classification of NAPs showed that the complex can tilt with respect to the cell membrane. A protein complex containing exclusively the proteins P140 and P110, was purified from M. genitalium and was structurally characterized by negative‐stain single particle EM reconstruction. The close structural similarity found between intact NAPs and the isolated P140/P110 complexes, shows that dimers of P140/P110 heterodimers are the only components of the extracellular region of intact NAPs in M. genitalium.     

Morphology and development of rhabdovirus-like particles inCuscuta odorata (Convolvulaceae) simultaneous infected with virus and mycoplasma-like organisms

Summary Electron microscopic examination ofCuscuta odorata, used for transmission trials, revealed mycoplasma-like organisms (MLO) as well as rhabdovirus-like particles, unknown toCuscuta. The virus infection is confined to certain phloem-parenchyma cells and a 1–2 cell thick layer of parenchyma cells with thickened walls surrounding the central cylinder. Virus particles, mostly bacilliform, could be detected mainly in the nucleus but also in the cytoplasm. They reach a length of 350–400 nm and a diameter of approximately 75 nm. Virus assembly takes place exclusively in the nucleus. Virus maturation occurs in membrane bound areas within the nucleus, which have no connection with the perinuclear space. Formation of nucleocapsids is always associated with a nuclear viroplasm. Envelopment of virus particles occurs in these membrane bound areas. Budding into the perinuclear space does not occur. Virus infection leads to degeneration and finally to death of the protoplast.Abbreviations cy cytoplasm - m membrane stacks - mt mitochondria - my mycoplasma-like organisms - nc nucleocapsid - ncp nucleocapsid particles - nf nuclear filaments - np nucleoplasm - nu nucleus - nvp nuclear viroplasm - oc obliterated cells - p plastid - pc passage cells - ph phloem - ps perinuclear space - spc strand of parenchymatous cells - v virus particle - x xylem     

Morphological changes of the optic lobe from late embryonic to adult stages in oval squids Sepioteuthis lessoniana

The optic lobe is the largest brain area within the central nervous system of cephalopods and it plays important roles in the processing of visual information, the regulation of body patterning, and locomotive behavior. The oval squid Sepioteuthis lessoniana has relatively large optic lobes that are responsible for visual communication via dynamic body patterning. It has been observed that the visual behaviors of oval squids change as the animals mature, yet little is known about how the structure of the optic lobes changes during development. The aim of the present study was to characterize the ontogenetic changes in neural organization of the optic lobes of S. lessoniana from late embryonic stage to adulthood. Magnetic resonance imaging and micro‐CT scans were acquired to reconstruct the 3D‐structure of the optic lobes and examine the external morphology at different developmental stages. In addition, optic lobe slices with nuclear staining were used to reveal changes in the internal morphology throughout development. As oval squids mature, the proportion of the brain making up the optic lobes increases continuously, and the optic lobes appear to have a prominent dent on the ventrolateral side. Inside the optic lobe, the cortex and the medulla expand steadily from the late embryonic stage to adulthood, but the cell islands in the tangential zone of the optic lobe decrease continuously in parallel. Interestingly, the size of the nuclei of cells within the medulla of the optic lobe increases throughout development. These findings suggest that the optic lobe undergoes continuous external morphological change and internal neural reorganization throughout the oval squid's development. These morphological changes in the optic lobe are likely to be responsible for changes in the visuomotor behavior of oval squids from hatching to adulthood.     

Monthly fluctuations in radial growth of individual lobes of the lichenParmelia conspersa (Erhr. ex Ach.) Ach.

The radial growth (RG) of 120 lobes from 35 thalli of the foliose lichenParmelia conspersa (Ehrh. ex Ach.) Ach. was studied monthly over 22 months in south Gwynedd, Wales, UK. Autocorrelation analysis of each lobe identified three patterns of fluctuation: I) random fluctuations (58% of lobes), 2) a cyclic pattern of growth (23% of lobes), and 3) fluctuating growth interrupted by longer periods of very low or zero growth (19% of lobes). In 80% of thalli, two or three patterns of fluctuation were present within the same thallus. Growth fluctuations were correlated with climatic variables in 31% of lobes, most commonly with either total rainfall or number of rain days per month. Lobes correlated with climate were not associated with a particular type of growth fluctuation. RG of a lobe was positively correlated with the degree of bifurcation of the lobe tip. It is hypothesised that lobes ofP. conspersa exhibit a cyclic pattern of growth due in part to lobe division. The effects of climate, periods of zero growth, and microvariationsin the environment of a lobe are superimposed on this cyclic pattern resulting in the random growth of many lobes. Random growth fluctuations may contribute to the maintenance of thallus symmetry inP. conspersa.     

Developmental puffing activity in the salivary gland and Malpighian tubule chromosomes ofAcricotopus lucidus (Diptera,Chironomidae)

A detailed map of the salivary gland chromosomes ofAcricotopus lucidus is presented. Differences in puffing and developmental Puffing sequences of the three salivary gland lobes were investigated from mid fourth larval instar to pupation and compared with the puffing pattern of the Malpighian tubules. The intraglandular differentiation is quite extensive; the differences in the pattern of gene activity between the anterior lobe and the main and side lobes are as great as between the salivary gland and the Malpighian tubules. In the main and side lobes all developmental puffing changes proceed synchronously whereas in the anterior lobe both asynchronous and synchronous changes occur. In the anterior lobe the asynchronous regression of BR 3 and BR 4 is followed by a characteristic sequence of activation and inactivation of puffs.     

Autonomous circular and radial motions of the nucleus inPleurenterium tumidum and their relation to cytoskeletal elements and the plasma membrane

Summary InPleurenterium tumidum the nucleus leaves its central position at the end of cell development and moves centrifugally towards the cortical cytoplasm of the isthmus area. It passes between the chloroplast lobes and starts to perform circular motions along the cell wall ring of the isthmus independently from other cell organelles and cytoplasmic streaming. This autonomous nuclear motion is a unique phenomenon in plant cells which is reported here for the first time. One turn of the nucleus which may occur either clockwise or counter-clockwise lasts an average of 60 minutes. The velocity of circular nuclear motion lies between 0.03 and 0.08 m per second and increases with increasing number of nuclear turns. The nucleus undergoes at least 12 but sometimes up to 70 turns and may change its direction of motion several times. When circular nuclear motion is finished the nucleus migrates centripetally towards the cell center where the next mitosis takes place.Ultrastructural studies demonstrate that a distinct arrangement of the plasma membrane forming a ring-shaped fold together with the adjacent isthmus system of microtubules (IS) serves as a hoop-like track for the nucleus during the stage of circular motion. The nucleus moves along this track by surrounding it in a deep furrow which develops parallel to its longitudinal axis at its cell wall facing side. The spatial arrangement of the plasma membrane fold and the nuclear furrow are only present during the stage of circular nuclear motion. No actin filaments seem to be involved in the nuclear circulations since the nucleus continues its circular motions after cytochalasin B (CB) treatment even at concentrations which arrest cytoplasmic streaming. Amiprophos-methyl (APM) leads to an inhibition of circular nuclear motion which resumes when the APM solution is removed. Microtubules appear to be primarily responsible also for both the radial nuclear motions as well as the anchoring of the nucleus in its central position. The meaning of circular and radial nuclear motions for thePleurenterium cell is not yet clear, a relation between the nuclear behavior and the inner cell architecture is discussed and compared to that of other desmids.     

Pigment-dispersing hormone (PDH)-immunoreactive neurons form a direct coupling pathway between the bilaterally symmetric circadian pacemakers of the cockroach Leucophaea maderae

Circadian locomotor activity rhythms of the cockroach Leucophaea maderae are driven by two bilaterally paired and mutually coupled pacemakers that reside in the optic lobes of the brain. Transplantation studies have shown that this circadian pacemaker is located in the accessory medulla (AMe), a small neuropil of the medulla of the optic lobe. The AMe is densely innervated by about 12 anterior pigment-dispersing-hormone-immunoreactive (PDH-ir) medulla (PDHMe) neurons. PDH-ir neurons are circadian pacemaker candidates in the fruitfly and cockroach. A subpopulation of these neurons also appears to connect both optic lobes and may constitute at least one of the circadian coupling pathways. To determine whether PDHMe neurons directly connect both accessory medullae, we injected rhodamine-labeled dextran as neuronal tracer into one AMe and performed PDH immunocytochemistry. Double-labeled fibers in the anterior, shell, and internodular neuropil of the AMe contralaterally to the injection site showed that PDH-ir fibers directly connect both accessory medullae. This connection is formed by three anterior PDHMe neurons of each optic lobe, which, thus, fulfill morphological criteria for a direct circadian coupling pathway. Our double-label studies also showed that all except one of the midbrain projection areas of anterior PDHMe neurons were innervated ipsilaterally and contralaterally. Thus, anterior PDHMe neurons seem to play multiple roles in generating circadian rhythms. They also deliver timing information output and perform mutual pacemaker coupling in L. maderae. This work was supported by the Deutsche Forschungsgemeinschaft (DFG) grants STE 531/7-1, 2, 3, and Human Science Frontier     

Corynoplastis japonica gen. et sp. nov. and Dixoniellales ord. nov. (Rhodellophyceae,Rhodophyta) based on morphological and molecular evidence

A new unicellular red alga, Corynoplastis japonica gen. et sp. nov., is described from Tobishima, Japan. Cells are spherical, 18–33 µm in diameter, pale purple to brownish red and surrounded by a mucilaginous sheath. A single chloroplast with many lobes extends from the cell periphery to the cell center. A peripheral thylakoid is present. A pyrenoid occurs at each innermost chloroplast lobe end and one or two thylakoids are present in the pyrenoid matrix. The nucleus is eccentric to peripheral and Golgi bodies are scattered throughout the cell and associated with endoplasmic reticulum. Cells have a slow random gliding motility. The low molecular weight carbohydrate mannitol is present in the cells. Molecular phylogenetic analysis indicates that this alga is closely related to members of the genus Rhodella. A new order, Dixoniellales, is established for Dixoniella, Neorhodella and Glaucosphaera based on molecular and ultrastructural evidence (Golgi bodies associated only with the nucleus). The redefined order Rhodellales in which Rhodella and Corynoplastis are placed is characterized ultrastructurally by Golgi bodies scattered throughout the cytoplasm and associated with endoplasmic reticulum.     

Nonrandom location and orientation of the inactive X chromosome in human neutrophil nuclei

The nuclei of human neutrophils typically consist of a linear array of three or four lobes joined by DNA-containing filaments. Terminal lobes are connected to internal lobes via a single filament, while internal lobes have two filaments, each to an adjacent lobe. Some lobes also have appendages of various shapes and sizes. In particular, up to 17% of neutrophil nuclei of healthy women exhibit a drumstick-shaped appendage that contains the inactive X chromosome. This report provides a detailed analysis of the relationship between nuclear morphology and the location of the X and Y chromosomes in human neutrophils. Fluorescent in situ hybridization analysis revealed that the X and the Y chromosomes of male neutrophil nuclei are randomly distributed among nuclear lobes. Similarly, in female neutrophil nuclei with a drumstick appendage, the active X chromosome is also randomly distributed among lobes. In contrast, the inactive X chromosome is preferentially located in a terminal lobe in over 90% nuclei with drumsticks. Within the terminal lobe of nuclei with drumsticks, the inactive X chromosome lies distal to the point of filament attachment in 80% of the nuclei. The inactive X chromosome also exhibits a specific orientation within the drumstick appendage, with over 95% of nuclei having the X centromere located toward the tip of the appendage. Female nuclei without a drumstick appendage also have one of the X chromosomes (presumably the inactive chromosome) preferentially situated in a terminal lobe. Nonrandom distribution of the inactive X chromosome is discussed in the context of a model that considers chromosomes as determinants of neutrophil nuclear morphology.     

Substructural morphogenesis of the spindle apparatus in meiotic basidia ofCoprinus micaceus (Agaricales)

The spindle apparatus ofCoprinus micaceus begins to develop from the diglobular polar body outside the nucleus. During both meiotic divisions it operates inside the nuclear envelope and consists of two amorphous poles, a central bundle of interpolar microtubules, and chromosomal microtubules. A metaphase plate cannot exist because the interpolar strand of fibers is persistent throughout the division process. Within the spindle axis more than 100 microtubules can be estimated. They are encircled by a ring of chromatic structures. During the telophase the former spindle pole is evaginated from the nuclear envelope and contacts the plasmalemma near the cell wall.     

Morphology of the foveal glands and foveae dorsales in male Hyalomma truncatum and Rhipicephalus evertsi mimeticus ticks (Acari; Ixodidae) before and during feeding

The ultrastructure of the foveae dorsales and foveal glands in unfed and attached male Hyalomma truncatum and Rhipicephalus evertsi mimeticus ticks was studied. Both species are provided with a paired foveal gland system, which is similar in unfed as well as in attached ticks. This gland system consists of the fovea dorsalis with pores and pore tubes as the external part, the foveal neck zone as a link between the fovea dorsalis and the lobes of the gland and the bulbous lobes as the innermost part. The fovea dorsalis is located on either side of the dorsal midline in the midsection of the body and appears as a roundish plate containing 15±6.5 and 21±7 slit-like pores in R. evertsi mimeticus (n=210) and H. truncatum (n=210), respectively. Each pore leads into a cuticular lined channel containing a pore tube. Below each fovea, the foveal neck zone is located within a groove of the cuticle and consists of the termini of the pore tubes which enlarge basally to form a cup-shaped ampulla each. Furthermore, secretory lobes are located below the foveal neck zone. Each lobe consists of secretory cells and a central excretory duct which leads into the ampulla. The ducts are lined with microvilli. The secretory cells contain numerous vesicles of varying size with one or more granules. In male ticks of both species the secretory lobe cells remained unchanged in size, structure and granule content irrespective of whether they were unfed or attached for up to 30 days. Axons occur in the fascicles between the secretory lobe cells containing numerous neurosecretory vesicles. A possible role of the foveal glands in the production of pheromones is hypothesized.     

Identificaton of UV,green and red receptors,and their projection to lamina in the cabbage butterfly,Pieris rapae

Summary The photoreceptors in the compound eye of a cabbage butterfly, Pieris rapae, were examined by conventional and intracellular-labeling electron microscopy by the use of the cobalt(III)-lysine complex as an ionized marker. Five types of spectral sensitivity were recorded intracellularly in electrophysiological experiments. They peaked at about 340, 380, 480, 560 and 620 nm, respectively. One of the distal retinula cells (R2) was a UV receptor, whereas the R4 distal retinula cell was a green receptor. The basal retinula cell, R9, was found to be a red receptor; it was localized near the basement membrane, having a bilobed cell body with an individual nucleus in each lobe. A small number of rhabdomere microvilli were present in a narrow cytoplasmic bridge connecting the two lobes. The axons of six retinula cells (R3–R8) in each ommatidium terminated at the cartridge in the lamina (short visual fiber), whereas those of the other three retinula cells, R1, R2 and R9, extended to the medulla (long visual fiber). The information from the UV and red receptors is therefore probably delivered directly to the medulla neurons, independent of that from the other spectral receptor types.     

The chloroplast and mitochondrial genomes of two Gomphonema parvulum (Bacillariophyta) environmental isolates from South Carolina (United States) and Virginia (United States)

Gomphonema parvulum is a cosmopolitan freshwater diatom that is used as an indicator in water quality biomonitoring. In this study, we report the culturing of two geographically separated isolates from southeastern North America, their morphology, and the sequencing and assembly of their mitochondrial and chloroplast genomes. Morphologically, both strains fit G. parvulum sensu lato, but the frustules from a protected habitat in South Carolina were smaller than those cited in the historic data of this species from the same location as well as a second culture from Virginia. Phylogenetic analyses using the rbcL gene placed both within a clade with G. parvulum. Genetic markers, including full chloroplast and mitochondrial genomes and the nuclear small subunit rRNA gene region were assembled from each isolate. The organellar genomes of the two strains varied slightly in size due to small differences in intergenic regions with chloroplast genomes of 121,035 bp and 121,482 bp and mitochondrial genomes of 34,639 bp and 34,654 bp. The intraspecific pairwise identities of the chloroplast and mitochondrial genomes of these two isolates were 97.9% and 95.4%, respectively. Multigene phylogenetic analysis demonstrated a close relationship between G. parvulum, Gomphoneis minuta, and Didymosphenia geminata.     

A Golgi study of the hypothalamus of Actinopterygii

Summary The posterior hypothalami of the polypteriform, Calamoichthys, and of the teleost, Anguilla, were studied by means of the Golgi technique. In Calamoichthys, the lateral lobes are not developed and the median lobe is simple. In Anguilla, the median (tuberal) lobe shows lophodendritic, CSF-contacting cells and horizontal cells in the periventricular grey and some reticular elements directed toward the cell-poor lateral areas. In the lateral lobes the periventricular grey is formed by multipolar neurons and a diffuse population of multipolar cells of uncertain identity. The nucleus diffusus lobi lateralis is formed by scarce multipolar neurons, often placed next to the external surface of the brain. The organization of the lateral lobes in Actinopterygii is reminiscent of highly developed integrative regions.Work performed under CNR Project Biology of Reproduction     

MITOSIS AND CYTOKINESIS IN THE PRASINOPHYCEAE. I. MANTONIELLA SQUAMATA (MANTON AND PARKE) DESIKACHARY

Mitosis in Mantoniella squamata (Manton and Parke) Desikachary, a small scale-covered green monad, is presented. Organelle replication precedes nuclear division and begins with the replication of the chloroplast. As the chloroplasts separate, the Golgi and flagellar apparatuses divide. The discoid microbody enlarges and becomes ‘V'-shaped, with the arms extending toward depressions in the pyrenoid stalks of the chloroplasts. At prophase, microtubules produced by an amorphous microtubule organizing center enter the nucleus via polar fenestre. The nuclear membrane remains intact. As the chloroplasts migrate further apart, the spindle pole-to-pole distance increases. By metaphase, daughter-cell lobes are discernible as a cleavage furrow, which appears as early as prophase, and begins to incise the cell. A single Golgi apparatus is situated near the spindle pole; the flagellar apparatus lies adjacent to the pole. The cleavage furrow continues to constrict the cell, resulting in a narrowing isthmus containing the elongate microbody, nucleus and a rootlet system connecting the basal bodies of the daughter flagella. At telophase, no extra-nuclear microtubular systems other than the previously observed rootlet are present and the nuclei remain separated from each other. In cells undergoing multiple divisions to produce more than two daughter cells, the orientation of organelles changes somewhat, with the basal bodies and the Golgi apparatus separating daughter nuclei prior to the onset of cytokinesis. The mechanics of mitosis in Mantoniella are compared with other green monads and the evolutionary implications discussed.     

The lobular division,bronchial tree and blood vessels of the squirrel monkey lung

The lobular division, bronchial tree, and blood vessels in lungs of seven squirrel monkeys (Saimiri sciureus) were examined from the viewpoint of comparative anatomy. The right lung of the squirrel monkey consists of the upper, middle, lower, and accessory lobes, whereas the left lung consists of the upper, middle, and lower lobes. These lobes are completely separated by interlobular fissures. In three of seven examples examined the left middle lobe was lacking. The squirrel monkey lung has four bronchiole systems, i.e. dorsal, lateral, ventral, and medial, on both sides. The upper lobes are formed by the first branches of the dorsal bronchiole systems. The middle lobes are formed by the first branches of the lateral bronchiole systems. The remaining bronchioles constitute the lower lobes. In addition to the above lobes, in the right lung, the accessory lobe is present, being formed by the first branch of the ventral bronchiole system. The right pulmonary artery runs across the ventral side of the right upper lobe bronchiole, and then across the dorsal side of the right middle lobe bronchiole. Thereafter, it runs between the dorsal bronchiole and lateral bronchiole systems along the dorso-lateral side of the right bronchus. During its course, the right pulmonary artery gives off the arterial branches which run along each bronchiole. These branches run mainly along the dorsal or lateral side of the bronchioles. In the left lung, the pulmonary artery and its branches run the same course as in the right lung. The pulmonary veins run mainly the ventral or medial side of the bronchioles, and between the bronchioles.