Light penetrance in lake kinneret

The characteristics of light penetrance in Lake Kinneret, Israel, were observed over the years 1970 to 1973. Light measurements were made concurrently with those of algal speciation and biomass, chlorophyll concentrations and primary production. Vertical extinction coefficients of green light (filter VG9), the most penetrating spectral component, ranged from 0.15 (August 1970) to 0.93 In units m^–1 (April 1970), reflecting the large differences between algal standing crops in non-bloom and bloom seasons. During the dinoflagellate bloom (Peridinium cinctum fa westii) from February through June, the increment of extinction coefficient per unit increase of chlorophyll concentration was 0.006 ln units mg^–1 m². The uneven vertical distribution of algae at this period caused irregularities in the depth curves of light penetrance. At other times, when the phytoplankton cells were more homogeneously dispersed with depth, regular light penetrance curves were observed; however, as previously noted (Rodhe, 1972), attenuation of algal photosynthetic activity often appeared to be regulated by the blue spectral component (filter BG 12). Ratios of absorbed to scattered light in the upper water column ranged from 85:15 to 75:25.     

Postnatal development of the pancreas in the opossum. Light microscopy.

The pancreas of the newborn opossum consists of a central region of forming islets surrounded by primitive tubules that end in proacinar cells. Paratubular buds, which are outgrowths from the tubular epithelium, characterize the newborn pancreas and eventually give rise to both exocrine and endocrine units. 4 days after birth, definite intralobular ducts, acini and centroacinar cells are observed. In addition to the central expanding islets (primary islets), endocrine cells are observed singly or in small groups in the ductal epithelium. The endocrine cells are believed to originate from the terminal cells of the ductal epithelium and, throughout the entire postnatal period, retain a close association with the exocrine epithelium. With the simultaneous proliferation of both endocrine and exocrine components from the ductal system, the majority of the islets observed at 24 days (5.0 cm) appear to be surrounded by a single layer of acinar cells. As acini develop and the ducts expand toward the periphery, this layer of acinar cells separates from the developing islets, the majority of which have become localized within the centers of lobules to form the secondary islets by the 10.0-cm stage (59 days). A marked development of lobules is observed by the 13.0-cm stage and the majority of acinar cells now are filled with zymogen granules. Acinar cells continue to proliferate late into the postnatal period and the majority of acini exhibit a tubular form in the juvenile and adult opossum.     

The karyosphere during late oogenesis in Rana ridibunda.

The organization of the nucleus in the oocytes of Rana ridibunda was examined during late diplotene at the light and electron microscopic level. At this stage the chromosomes are relatively condensed and assembled in the centre of the nucleus, constituting a karyosphere. The chromosomes here are associated with the central "protein sphere" (15--20 microns in diameter), obviously at their telomeres. Numerous nucleoli are accumulated around the chromosomes, forming a karyosphere capsule and contain segregated fibrillar and granular components; structures resembling perinucleolar chromatin and fibrillar bodies (spherules) are associated with the nucleoli. Granules 30 to 40 nm in diameter are seen to surround the fibrillar spherules. "Nucleolus-like bodies" consisting of granules 10 to 15 nm in diameter which are embedded in finely fibrillar material are often associated in contact with the chromosomes. The central sphere is an accumulation of annular structures similar to those of the pore complexes of the nuclear envelope. These structures are bound to the chromosome material, the "nucleolus-like bodies" and the fibrillar bodies. A participation of "nucleolus-like bodies" in the formation of the central sphere is suggested. A possible role of the nuclear protein matrix in the construction of the karyosphere elements is discussed.     

Postnatal development of the dog pineal gland. Light microscopy

The light microscopical morphology of the dog pineal gland from the first postnatal day to maturity is described. In the first postnatal week, the pineal parenchyma shows immature cells and many mitotic figures. In this week, pigmented cells are observed for the first time, both in the pineal gland and in extrapineal nodules. Throughout the second week, the pineal parenchyma shows a cordonal pattern that disappears progressively in the following stages. From the 20-30th day onward, it is feasible to discern the cell types characteristic for the adult pineal gland. In the adult animals, the length of the pineal gland axes almost quadruplies that of the pineal gland in neonatal stages. The light microscopical features of the adult dog pineal gland are also described.     

Light and electron microscopy on the sporulation of the oocysts of Eimeria brunetti. I. Development of the zygote and formation of the sporoblasts

The initial stages of sporulation in oocysts of Eimeria brunetti were examined in samples sporulated at 27 degrees C for 0, 12 and 24 hours. The initial zygote was found to be roughly spherical and to contain a number of polysaccharide granules which were congregated in one region of the organism. The cytoplasm also contained some strands of rough endoplasmic reticulum together with a number of mitochondria, some Golgi bodies, and some electron translucent vacuoles. The nucleus was large, with amorphous nucleoplasm and a nucleous. The cytoplasmic mass of the zygote was limited by a single unit membrane which possessed some micropores. After initiation of the sporulation, the metabolic activity of the organism appeared to increase as evidenced by the augmentation in the cytoplasm of the amounts of rough endoplasmic reticulum, number of Golgi bodies, and the appearance of polyribosomes. However, at this stage, the presence of large spherical bodies (anlagen of the refractile bodies of the sporozoites) constituted the most obvious change in the cytoplasm of the organism. After nuclear division the daughter nuclei were situated well separated in the cytoplasm and the polysaccharide granules were evenly distributed throughout the cytoplasm of the zygote. Eventually four sporoblasts were formed by invaginations of the limiting membrane. Each sporoblast was limited by a unit membrane and contained a nucleus, and the same cytoplasmic organelles as found in the zygote. The development of the sporoblast was initially accompanied by the appearance of a second limiting membrane.     

Light and electron microscopy on the sporulation of the oocysts of Eimeria brunetti. II. Development into the sporocyst and formation of the sporozoite

The later stages of sporulation in oocysts of Eimeria brunetti were examined in samples which had been allowed to sporulate at 27 degrees C for 24, 36 and 48 hours. It was observed that the sporoblasts became ellipsoidal and the nucleus underwent the final division. A nucleus with associated Golgi bodies was not observed at either end of the organism. The cytoplasm was limited by two unit membranes and contained rough endoplasmic reticulum, dense bodies, electron translucent vacuoles and mitochondria. The first evidence of sporozoite formation was the appearance of a dense plaque at either end of the organism. This appeared in the vicinity of the nuclei, and adjacent to the limiting membrane of the soroblast. At this stage the sporocyst wall was still unformed. Then the two sporozoites were formed from opposite ends of the organism by growth of the dense plaques and invaginations of the plasmalemma which thus formed the pellicles of the developing sporozoites. A conoid and subpellicular microtubules were observed at this stage as development continued, a number of vacuoles were found between the nucleus and the conoid. These vacuoles constituted the precursors of the rhoptries and micronemes. At the same stage a large dense body had appeared within the forming sporozoite. As the sporozoite developed, this body, anterior refractile body, is followed by the nucleus and another dense body which formed the posterior refractile body. During this period, the thin sporocyst wall was formed and Stieda and sub-Stieda bodies were now present at one end of the sporocyst. Each mature sporocyst contained two sporozoites.     

Electron microscopy of ascus formation in the yeast debaryomyces hansenii.

Ascus formation in Debaryomyces hansenii includes fusion of two cells, usually mother and daughter while still attached to each other, through short protuberances developed from the cross wall between them. Nuclear fusion takes place in the channel connecting the two cells; meiosis apparently occurs in the mother cell. Generally, only one lobe of the meiotic nucleus is surrounded by a prospore wall and it becomes the nucleus of a spore with a warty wall. The rest of the nucleus disappears. The spores germinate by swelling in the ascus and forming one or more buds.     

Nuclear ultrastructure of the oocytes from human antral follicles. Formation of the karyosphere

The organization of the nucleus in the oocytes from human antral follicles was examined at the electron microscopic level. At this time all the chromosomes are aggregated around an inactivated nucleolus forming a karyosphere 5-7 micron in diameter. The nucleolus bears no granular component and consists of densely packed delicate fibrillar material. The peripheral zone resembling a ring 0.5 micron thick is separated in the nucleolus. Nucleolus-like bodies (NLB), consisting of granules 20 nm in diameter embedded in finely fibrillar material, are constantly observed in contact with the chromatin. The eventually formed karyosphere is a complex of intimately interconnecting structures--the nucleolus, chromosomes and NLB. However, the chromatin surrounding the nucleolus does not form a continuous (compact) mass as it is observed at the light microscopic level. It is determined that the human karyosphere is formed during the preovulatory period when the connection between oocyte and follicular cells of cumulus oophorus is lost. The duration of karyosphere existence in the human oocytes, and relation of the karyosphere to the processes of antral follicle atresia are discussed.     

Ice crystals formed in tissues during cryosurgery. I. Light microscopy

The size and distribution of ice crystals formed during cryosurgical procedures in intact animals are not clear. In the present experiment oral mucosa was frozen in situ by means of a surface applied cold probe and was excised and freeze substituted while in the frozen state. It was shown that the form of the frozen tissue was preserved during this procedure and the area frozen was divisible into a zone representing the central part of the lesion and a peripheral zone separating this from normal tissue. Ice crystals within the body of the lesion were intracellular in location but varied somewhat in size. Ice crystals in the boundary zone appeared to be intracellular in the epithelium and both intra- and extracellular in the muscle fibres.It is suggested that the intracellular crystals in the body of the frozen area result in cell death while the extracellular ice in the boundary zone results in a less predictable response.