THE FINE STRUCTURE AND FUNCTION OF THE CONTRACTILE AXOSTYLES OF CERTAIN FLAGELLATES

The axostyles of the flagellates Oxymonas, Saccinobaculus, and Notila are large ribbon-shaped structures which undulate actively in the cytoplasm. The form of their movements is described and illustrated. Axostyles consist of regular arrays of longitudinal fibres, the number of which varies between 100 and 5000 in different species. The fibres are about 240 A in diameter, apparently hollow, regularly cross-banded with a periodicity of about 150 A, and connected by delicate cross-links, also at regular intervals of about 150 A. They resemble very closely the central fibres of cilia and flagella. No other structural components are present, except at the anterior end, where the fibres are attached to one or more basal bodies, and at the posterior tip, where they are anchored to the plasma membrane. The relevance of the findings to an understanding of the mechanism of ciliary and flagellar movements is discussed.     

ASPECTS OF CILIARY FINE STRUCTURE IN EUPLOTES PATELLA

1. The functional unity of cirri and membranelles can result structurally only from extensions of the ciliary membrane. 2. The pellicle is composed of an outer pellicular membrane and an inner cytoplasmic membrane. 3. The ciliary rootlets are composed of numerous filaments 120 A in diameter with central areas of low density. They have no periodic structure. 4. The ciliary membrane is a double-layered structure continuous with the pellicular membrane. The cilia show the typical arrangement of nine double, peripheral and two single, central fibrils. All fibrils pass into the basal region, the peripheral ones joining with the rootlet filaments, while the central fibrils from the extreme proximal position of the basal region turn back toward the pellicle and appear to unite just beneath the cytoplasmic membrane. 5. The cilia (300 mµ diameter) taper at their tips to a diameter at least as small as 50 mµ. At a diameter of about 150 mµ, the fibrils begin to show a reduction in number. 6. The central ciliary fibrils may determine the possible directions of ciliary beat. These fibrils show an intrafibrillar structure in their basal portion, which involves regularly spaced 40 A granules. 7. These observations on Euplotes, together with the other evidence cited, are consistent with the hypothesis that ciliary motion is produced by the contraction of the peripheral fibrils, while the central fibrils perhaps determine the plane in which the cilia can bend.     

FINE STRUCTURE CHANGES DURING FUNCTION OF THE DIGESTIVE GLAND OF VENUS'S-FLYTRAP

Changes in the structure of the digestive gland cells of Venus's-flytrap during the digestive process have been studied with light and electron microscopy. Large vacuolar lipid-protein inclusions break up and become smaller; however, they never completely disappear during the entire 7-10-day cycle. Dictyosomes in the resting digestive gland are associated with small, inconspicuous vesicles, whereas during the digestive cycle two types of prominent vesicles are observed on the peripheral tubules. Changes in plastid fine structure are complex and involve the disappearance of lipid globules and the tubular complex, followed by the formation of microtubules on the thylakoids and cisternae on the outer plastid membrane. Mitochondrial fine structure changes from the small cristae and light matrix of the resting state to large cristae and a very dense matrix representative of a change to a state where phosphorylation is tightly coupled to electron transport. Pronounced changes which occur in the cell envelope (cell wall and membrane taken together) are apparently associated with secretion of the digestive fluid. Numerous other changes are observed such as polysome formation, multivesicular body formation, mitochondria division, and changes which can be attributed in general to elevated cell activity.     

THE FINE STRUCTURE AND FUNCTION OF THE SALIVARY GLANDS OF NUCELLA LAPILLUS (GASTROPODA: MURICIDAE)

The fine structure of the tubular and acinous salivary glandsof Nucella lapillus (L.) has been studied and some histochemicaland enzyme tests have been carried out. The clusters of subepithelialcells of the tubular glands secrete a glycoprotein composedof chains of tubular macromolecules resembling secretions knownto have adhesive properties which may assist in boring. Thesecretion is rich in disulphide groups, as are many toxins,and is believed to be responsible for the recently demonstratedpharmacological activity of the glands. It is proposed thatflaccid paralysis is induced in prey by envenomation with thissecretion during rasping, after soft parts have been exposedby an ‘anti-predator’ reaction to secretion fromthe hypobranchial gland of Nucella. The secretory vesicles ofboth types of gland cells in the acinous glands have heterogeneouscontents indicating that their secretions are complex. The majorcomponent in those of the mucous cells is an acid mucopolysaccharidetypical of a lubricant or releasing agent. The ciliated basalcells resemble typical enzyme-secreting cells and the majorconstituent of their secretion is a finely granular glycoprotein. (Received 8 January 1990; accepted 5 June 1990)     

THE FINE STRUCTURE OF CAPILLARIES AND SMALL ARTERIES

Details of capillary endothelia of the mammalian heart are described and compared with capillaries of other organs and tissues. Continuous invagination and pinching off of the plasma membrane to form small vesicles which move across the cytoplasm are suggested as constituting a means of active and selective transmission through capillary walls (12). This might be designated as cytopempsis (transmission by cell). The fine structure of the different layers in the walls of small heart arteries is demonstrated. Endothelial protrusions extend through windows of the elestica interna to make direct contact with smooth muscle plasma membranes. The elastica interna appears to vary greatly in both thickness and density, and probably restricts filtration, diffusion, and osmosis to such an extent that windows and the transport mechanisms described (cytopempsis) are necessary for the functional integrity of the smooth muscle layer. The contractile material consists of very fine, poorly oriented filaments.     

THE FUNCTION OF THE BRAIN IN LOCOMOTION OF THE POLYCLAD WORM,YUNGIA AURANTIACA

Coordinated swimming movements in Yungia are not dependent upon the presence of the brain. The neuromuscular mechanism necessary for spontaneous movement and swimming is complete in the body of the animal apart from the brain. Normally this mechanism is set in motion by sensory stimulation arriving by way of the brain. The latter is a region of low threshold and acts as an amplifier by sending the impulses into a great number of channels. When the head is cut off these connections with the sensorium are broken, consequently peripheral stimulation does not have its usual effect. If, however, the motor nerves are stimulated directly as by mechanical stimulation of the median anterior region, then swimming movements result. Also if the threshold of the entire nervous mechanism is lowered by phenol or by an increase in the ion ratios See PDF for Equation and See PDF for Equation then again peripheral stimulation throws the neuromuscular mechanism into activity and swimming movements result.     

SECRETORY CELLS OF LILY PISTILS. I. FINE STRUCTURE AND FUNCTION

The fine structure of the cells which line the canal of Lilium longiflorum pistils confirms the secretory function which has been ascribed to them. The cells differ in structure from the secretory cells which cover the stigma surface and are therefore referred to as canal cells rather than stigmatoid cells. Their most striking feature is an elaborate wall, 8–14 μ in maximum depth, on the side facing the canal, which with associated structures, we term the secretion zone. Pollination, which triggers chemotropic activity in the style and secretory activity in the canal cells, is not correlated with marked changes in the fine structure of the canal cells. The canal cells appear to fit well into that category which Gunning and Pate have termed “transfer cells.”     

FINE STRUCTURE OF THE EYE OF A CHAETOGNATH

Electron microscopy reveals a star-like pigment cell at the center of the eye of the arrow-worm, Sagitta scrippsae. Between the arms of the pigment cell are clusters of photoreceptor cell processes, each process consisting of: (1) a tubular segment containing longitudinally arranged microtubules about 500 A in diameter and 20 µ in length; (2) a remarkable conical body, composed of cords and large granules, situated at the base of the tubular segment; and (3) a connecting piece which, like that of rods and cones, connects the process with the sensory cell proper and through which runs a fibrillar apparatus consisting of nine peripheral double tubules. Beneath the connecting piece lies a typical centriole with a striated rootlet. The receptor cell process is deeply recessed into the sensory cell which may possess a corona of microvilli at its inner surface. A nerve fiber arises from the outer end of the cell and passes into the optic nerve. Additional features are some supporting cells, an external layer of flattened epithelial cells, and an over-all investment of basement membrane and thick fibrous capsule. The fine structure and function of these elements of the eye are discussed in relation to earlier studies with the light microscope. The ciliary nature of the photoreceptor cell process in S. scrippsae points to a probable evolutionary relationship of chaetognaths to echinoderms and chordates.     

ON THE FINE STRUCTURE AND COMPOSITION OF THE NUCLEAR ENVELOPE

Nuclei from nearly ripe eggs of Rana pipiens were isolated and cleaned in 0.1 M KCl. The whole nucleus was then digested to various degrees with ribonuclease or trypsin, followed by washing and fixation in either osmium tetroxide or potassium permanganate. The nuclear envelope was dissected off, placed on a grid, air dried, and compared with undigested controls in the electron microscope. Some envelopes were dehydrated, embedded in methacrylate, and sectioned. Annuli around "pores" are composed of a substance or substances, at least partially fibrillar, which is preserved by osmium but lost during permanganate fixation. Material within the "pores" is also preserved by osmium but partially lost after permanganate. No evidence of granules or tubules in the annuli was found in air dried mounts although a granular appearance could be seen in tangentially oriented thin sections. Thin sections of isolated envelopes give evidence of diffuse material within the "pores" as well as a more condensed diaphragm across their waists. In whole mounts of the envelope the total density within "pores" is relatively constant from "pore" to "pore." All material within "pores," including the condensed diaphragm, is removable by trypsin digestion. Wispy material from the "pore" structure projects into the nucleus and annular material extends into the cytoplasm. Both annular and diaphragm materials remain with the envelope when it is isolated and are thus considered a part of its structure, not merely evidences of material passing through. There is no evidence of ribonuclease-removable material in any part of the "pore" complex.     

FINE STRUCTURE AND REPLICATION OF THE KINETOPLAST OF TRYPANOSOMA LEWISI

The kinetoplastic DNA of Trypanosoma lewisi is described as a filamentous body lying within a mitochondrion, with the filaments oriented parallel to the long axis of the cell. The manner of fixation, the replicative state, and perhaps the physiological state of the cell, may result in slight morphological differences among such bodies. The kinetoplastic DNA replicates to form "left" and "right" rather than "upper" and "lower" members, and both the kinetoplast and nucleus incorporate radiothymidine as shown by radioautography. Radioautographic analyses suggest a random incorporation of radiothymidine by kinetoplasts. Silver grains were occasionally observed over centriolar elements. Finally, the observations are discussed with respect to the sequential replication of the aforementioned organelles by T. lewisi.     

THE FINE STRUCTURE OF NEURONS

1. Thin sections of representative neurons from intramural, sympathetic and dorsal root ganglia, medulla oblongata, and cerebellar cortex were studied with the aid of the electron microscope. 2. The Nissl substance of these neurons consists of masses of endoplasmic reticulum showing various degrees of orientation; upon and between the cisternae, tubules, and vesicles of the reticulum lie clusters of punctate granules, 10 to 30 mµ in diameter. 3. A second system of membranes can be distinguished from the endoplasmic reticulum of the Nissl bodies by shallower and more tightly packed cisternae and by absence of granules. Intermediate forms between the two membranous systems have been found. 4. The cytoplasm between Nissl bodies contains numerous mitochondria, rounded lipid inclusions, and fine filaments.     

GENETIC STRUCTURE OF THE WESTERN NORTH AMERICAN AQUATIC GASTROPOD GENUS TAYLORCONCHA AND DESCRIPTION OF A SECOND SPECIES

The Bliss Rapids Snail (Taylorconcha serpenticola) is a threatenedspecies that ranges along a short reach of the middle SnakeRiver in southern Idaho. Additional Taylorconcha populationsof uncertain taxonomic status have recently been discoveredin other portions of the Snake River basin (Owyhee River, lowerSnake River). We investigated the phylogenetic relationshipsand population structure of these snails, together with twooutgroups, using cytochrome c oxidase subunit I (COI) of mitochondrialDNA and the first internal transcribed spacer region betweenthe 18S and 5.8S ribosomal DNA. These data show no sharing ofhaplotypes or genotypes among T. serpenticola and the Owyhee-LowerSnake populations, with both depicted as monophyletic unitswithin the Taylorconcha clade. Both of these datasets and morphologicalevidence suggest that the Owyhee-Lower Snake populations area distinct species, which we describe herein (T. insperata newspecies). Application of an available COI molecular clock suggeststhat Taylorconcha arose in the late Miocene, when ancestralSnake River drainage was impounded in an extensive lacustrinesystem (‘Lake Idaho’) in western Idaho. The shallowpopulation structuring of T. insperata suggests that the lowerSnake River was only recently colonized subsequent to incisionof Hells Canyon, draining of Lake Idaho, and development ofa through-going river in the late Neogene. The absence of significantgenetic structure in T. serpenticola, which is attributed tothe unstable course and flow regime of the middle Snake Riverduring the Quaternary, suggests that this species can be treatedas a single management unit. (Received 14 July 2005; accepted 23 September 2005)     

ANATOMY,HISTOCHEMISTRY AND FINE STRUCTURE OF THE GERMINATING EMBRYO OF PAULOWNIA TOMENTOSA

The anatomy, morphology and gross histochemistry of the germinating embryo and seedling of Paulownia tomentosa (Scrophulariaceae) is described. Cytohistological changes in the shoot apex are correlated with anatomical and histochemical differences. During the first days of germination and before leaf primordia are formed, there is a gradual increase in staining for cytoplasmic protein and RNA. Once the first leaves are initiated, the staining for these compounds remains constant in the central mother-cell zone, and further increase in protein and RNA is confined to the developing leaf primordia. Starch grains are found in all areas of the very young apex, but with anatomical maturity the grains are restricted to the central mother-cell zone. Some electron micrographs point up special cytological features.