Early Metamorphic Stage Research Articles

Ultrastructural study of the retinal pigment epithelium during metamorphosis in the sea lamprey (Petromyzon marinus L.)

The sequence of morphological changes in the retinal pigment epithelium during the metamorphic period of the sea lamprey Petromyzon marinus L. has been investigated using electron microscopy. At early metamorphic stages (stages I and II), photoreceptors are present in a small zone of the retina. During these stages, the lateral surface of the epithelial cells shows zonulae occludentes and adhaerentes. The degree of cell differentiation varies throughout the retinal pigment epithelium. Cells covering the differentiated photoreceptors in the central retina have phagosomes, whereas pigment granules appear only in the retinal pigment epithelium dorsal to the optic nerve head. Most epithelial cells have myeloid bodies; their morphology is more complex around the optic nerve head. At stage III, when photoreceptors develop over the whole retina, the distribution of cytoplasmic organelles is almost homogeneous in the retinal pigment epithelium. Subsequently, the basal plasma membrane of the epithelial cells becomes progressively folded and their apical processes enlarged. In addition, extensive gap junctions develop between retinal pigment cells. In late metamorphic stages, noticeable growth of myeloid bodies occurs and consequently the retinal pigment epithelium resembles that of the adult. This study also describes, for the first time, the presence of wandering phagocytes in the retinal pigment epithelium of lampreys; their role in melanosome degradation is discussed.

Plutonism, deformation, and metamorphism in the Proterozoic Flin Flon greenstone belt, Canada: Limits on timing provided by the single-zircon Pb-evaporation technique

The authors have used the single-zircon Pb-evaporation technique to determine the age of granitoids in the western Flin Flon domain of the Trans-Hudson orogen in Canada and to constrain the timing of molasse sedimentation, deformation, metamorphism, and mesothermal gold mineralization. The plutons were intruded between 1,860 and 1,834 Ma, about 30 m.y. after volcanism, and provide further evidence of a major period of intrusive activity throughout the Trans-Hudson orogen at that time. The older plutons (1,860 to 1,848 Ma) are synchronous with P2 deformation and the early stages of peak metamorphism, whereas the younger plutons are synchronous with or postdate the P3 deformation event. Molasse sedimentary units are deformed and metamorphosed; thus, deposition must have begun at about 1,860 Ma. Mesothermal gold mineralization postdates all plutons and may be related to high-grade peak metamorphism in adjacent terranes at about 1,815 Ma. This study also provides further support for the use of the Pb-evaporation technique as a suitable method for dating single zircons and indicates that the {sup 208}Pb/{sup 206}Pb ratio of zircons may be a useful tool in detecting the presence and source of xenocrystic zircons.

Schorl-dravite-ferridravite tourmalines deposited by hydrothermal magmatic fluids during early evolution of the Larderello geothermal field, Italy

Electron microprobe and petrographic data on tourmaline-rich assemblages, in addition to available data from fluid inclusions and geochronological studies, are used to model the early stage of hydrothermal metamorphism in the Larderello geothermal field, Italy. During this early stage different hydrothermal events are characterized by deposition of tourmaline, biotite, calcic plagioclase, K feldspar, quartz, and pyrrhotite at lithostatic pressures of 0.75 to 1 kbarsand temperatures in the range 400 degrees to 600 degrees C. Pressures exceeding hydrostatic values and inferred temperatures of 450 degrees to 460 degrees C at the bottom of well San Pompeo 2 suggest a possible present-day deposition of tourmaline in the deepest levels of the central and hottest part of the field.Hydrothermal tourmalines appear to have crystallized at temperatures in excess of 370 degrees C. They show significant replacement of Al by Fe (super +3) in the Z site, substitutions of Al for Si in the tetrahedral site, and slight vacancies in the X and Y sites produced by limited cation- and proton-deficient substitutions.In the hydrothermal tourmaline nearest to the inferred granitic contact and in the tourmaline of a leucogranitic dike crossed by well VCll, a negative correlation existing between Mg and Fe (super +2) reveals significant reciprocal substitutions of these elements in the Y site.Tschermak9s and aluminobuergerite substitutions and an increase in the molecular fractions of schorl and elbaite in the schorl-dravite and schorl-elbaite solid solutions were observed from rim to core of the VCll magmatic tourmalines. Rims and intermediate growth zones of magmatic tourmalines and most of the hydrothermal tourmalines have compositions falling in the field of metamorphic tourmalines. This behavior reveals the dominant control of the host rock on fluid chemistry.Some growth zones and most cores have compositions that plot in the field of tourmalines from granitoids. A gradual schorl or ferridravite enrichment from magmatic to hydrothermal tourmalines with increasing distance from the granite contact is also present. In a microprobe traverse from the base to the tip of an acicular tourmaline, four peaks of Fe (super +3) replacing Al can be ascribed to four distinct hydrothermal events generated by episodic ascent from below of magmatic fluids that became more and more oxidized with increasing distance from the granite contact, owing to an easier hydrogen leakage in the shallower and more fractured levels.The studied mineral assemblages and available fluid inclusion data reveal close analogies between the deepest and hottest part of the Larderello geothermal system and quartz-tour-maline and K silicate alteration zones of porphyry tin and copper deposits. The mineralizing fluids are inferred to have been of magmatic origin and were characterized by T = 400 degrees to 600 degrees C, pressure varying between hydrostatic (0.2-0.35 kbars) and lithostatic (0.75-1 kbars), commonly near lithostatic values, high f (sub O 2 ) as inferred by the presence of hematite and anhydrite among fluid inclusion daughter minerals, and very high salinities (up to 50-60 equiv wt % NaCl).

Counterclockwise P-T-t Paths from Amphibolites, Franciscan Complex, California: Relics from the Early Stages of Subduction Zone Metamorphism

Overprinting mineral relationships in amphibolites from the Franciscan Complex, California suggest metamorphic evolution from high-temperature amphibolite facies to the blueschist facies with increasing P/T ratio, a counterclockwise P-T-t path. Early formed pargasitic amphiboles are both crosscut and rimmed by subcalcic hornblendes that are, in turn, cut or rimmed by sodic amphiboles. Some amphibolites are overprinted successively by eclogite and blueschist facies assemblages. Clinopyroxenes are zoned with increasing jadeite component from core to rim. Multiple generations of phengites are present in the same sample and are more Si-rich with each successive generation of growth. Garnets in eclogite-overprinted amphibolites are zoned with an initial MgO increase away from the core to a maximum MgO zone followed by MgO decrease toward the rim. Garnets in other amphibolites show continually increasing MgO from core to rim. Several samples, representative of the variety of Franciscan amphibolites, are described in detail. The best-constrained sample exhibits a calculated P-T trajectory from 626-664°C at 9.2-10 kb for early amphibolite metamorphism to 496-537°C at 11.2-11.8 kb eclogite metamorphism to 300-350°C at >6.5-7 kb for final blueschist overprint. Overprinting mineral assemblages in other samples, as well as most Franciscan amphibolites described by other workers, are qualitatively, and in some cases quantitatively, suggestive of the same type of P-T trajectory. Geochronologic, textural, and petrologic data indicate that the overprinted amphibolites are probably the product of a single metamorphic event rather than a consequence of separate metamorphic episodes, but additional age dating is desirable for better confirmation. Amphibolite to blueschist facies metamorphic evolution may have taken place within 5 Ma. The following model is presented for the evolution of Franciscan amphibolites: (1) The amphibolites were metamorphosed as a dynamothermal aureole underneath the hanging wall of a subduction zone at the inception of subduction. (2) The amphibolites were then accreted to the upper plate. (3) Subsequent subduction and underplating of cold material insulated the hanging wall and allowed the upper plate and amphibolite to cool at depth, with the development of metamorphic assemblages of increasing P/T ratio. (4) Subduction beneath the accreted amphibolite may have broken up the amphibolite sheet, dragging blocks deeper down the subduction zone, leading to the pressure increase with cooling that is recorded by some of the samples. Deeper burial by thrusting within the upper plate after amphibolite metamorphism may also explain the pressure increase. The P-T trajectory of these rocks is consistent with P-T paths derived from published thermal models for similar tectonic settings.

Snowpack structure and avalanching, Craigieburn Range, New Zealand

Abstract A study of the seasonal development of the snowpack at 1700 m elevation in the Craigiebum Range, New Zealand, has revealed three phases of snowpack development. This phased development is considered in relation to snow avalanching. Analysis of a short period of continuous snowpack temperature gradient data has shown that temperature gradients exceed those generally required for recrystallisation processes, as evidenced by the common occurrence of temperature gradient forms in the snowpack. Partially metamorphosed new snow, especially clusters of rimed needles, and snow in the early stages of temperature gradient metamorphism, are weak in shear and frequently appear in avalanche sliding layers. Weak snowpack stratigraphies resemble those found for Northern Hemisphere inland-continental and coastal-maritime snow climates. Three categories of potential sliding layers for avalanche release are suggested. These are: (1) weaknesses in new snow stratigraphy, (2) weaknesses at old snow surfaces, and (3) ...

Metamorphism of an Early Palaeozoic continental margin, western Baie Verte Peninsula, Newfoundland

Metamorphic mineral assemblages and textures from Early Palaeozoic continental margin rocks in north‐western Newfoundland indicate that different structural levels have contrasting metamorphic histories. Rocks of the East Pond Metamorphic Suite, which represent the older, structurally lower level of the margin, experienced an early high‐pressure–low‐temperature stage of metamorphism (10–12 kbar minimum, 450–500°C) which produced eclogite in mafic dykes and phengite–garnet assemblages in pelites. This was overprinted by higher temperature–lower pressure amphibolite facies metamorphism (700–750°C, 7–9 kbar minimum) which produced complex symplectic textures in rocks of all compositions. Rocks of the Fleur de Lys Supergroup, which were deposited in the stratigraphically higher levels of the rifted margin, reached pressures of 7–8.5 kbar at about 450°C during the early stages of metamorphism, overprinted by assemblages which indicate maximum temperatures of 550–600°C at about 6.5 kbar. The metamorphic history of both units is interpreted to be the result of thermal relaxation following initial burial of a continental margin by overriding thrust sheets. Since there is no evidence that maximum pressures or temperatures within the Fleur de Lys Supergroup were ever as high as those reached in the East Pond Metamorphic Suite, these rocks may have followed parallel, ‘nested’P–T–t paths, with the more deeply buried East Pond Metamorphic Suite subjected to greater thermal relaxation effects. Quantitative modelling of P–T–t paths is not possible with the present data, owing to both large uncertainties in P–T estimates, and in the time of metamorphism.

Synthetic fluid inclusions ‐ VII. Re‐equilibration of fluid inclusions in quartz during laboratory‐simulated metamorphic burial and uplift

ABSTRACT P‐T conditions inferred from fluid inclusions in metamorphic rocks often disagree with the values predicted from mineral equilibria calculations. These observations suggest that inclusions formed during early stages of regional metamorphism continue to re‐equilibrate during burial and subsequent uplift in response to differential pressure. P‐T conditions accompanying burial and uplift were experimentally simulated by initially forming pure H2O inclusions in quartz at elevated temperatures and pressures, and then re‐equilibrating the inclusions in the presence of a 20 wt% NaCl solution such that final confining pressures ranged from 5 kbar above to 4 kbar below the initial internal pressure of the inclusions at the temperature of re‐equilibration.In all samples re‐equilibrated at confining pressures below the internal pressure, some inclusions were formed that had compositions of 20 wt% NaCl and densities in accord with the final P‐T conditions. Additionally, some inclusions were observed to contain fluids of intermediate salinities (between 0 and 20 wt% NaCl). Densities of these inclusions were also consistent with formation at the re‐equilibration P‐T conditions. The remainder of the fluid inclusions observed in these samples contained pure H2O and their homogenization temperatures corresponded to densities intermediate between the initial and final P‐T conditions. In short‐term experiments (7 days) where the initial internal overpressure exceeded 1 kbar, no inclusions were found that contained the original density and none were found to have totally re‐equilibrated. Instead, most H2O inclusions re‐equilibrated until their internal pressures were between ∼750 and 1500 bars above the confining pressure, regardless of the initial pressure differential. In a long‐term experiment (52 days), inclusions re‐equilibrated at a lower confining pressure than the initial internal pressure displayed homogenization temperatures corresponding to a range in final internal pressures between 0 kbar (i.e. total re‐equilibration) and 1.2 kbar above the confining pressure.In experiments where the confining pressure during re‐equilibration exceeded the initial internal pressure, densities of pure H2O inclusions increased to values intermediate between the initial and final P‐T conditions. Additionally, these inclusions were generally surrounded by a three‐dimensional halo of smaller inclusions, also of intermediate density, resulting in a texture similar to that previously ascribed to decrepitation from internal overpressure. In extreme cases where confining pressures were 4–5 kbar above the initial pressure, the parent inclusion almost completely closed leaving only the three‐dimensional array of small (5 μm) inclusions, the outline of which may be several times the volume of the original inclusion. Groups of such inclusions closely resemble textures commonly observed in medium‐ to high‐grade metamorphic rocks.Inclusions containing 10 and 42 wt% NaCl solutions trapped at 600 °c and 3 kbar were re‐equilibrated at 600 °c and 1 kbar for 5 days in dry argon to evaluate the importance of H2O diffusion as a mechanism of lowering the inclusion bulk density. Salinities of re‐equilibrated inclusions obtained from freezing point depressions and halite dissolution temperatures indicate that original compositions were preserved. Density changes similar to those previously described were noted in these experiments, in inclusions showing no visible microfractures. Therefore, density variations observed in inclusions in this study, re‐equilibrated under rapid deformation conditions, are considered to result from a change in the inclusion volume, without significant loss of contents by diffusion or leakage.

Stratiform tourmalinites in the Archaean tungsten province of West Greenland

In the Archaean Malene supracrustal rocks of West Greenland different types of stratiform tourmalinites have been found. The present article describes schistose anthophyllite-rich tourmalinites hosted in anthophyllite-cordierite schists. It is shown that the boron is of submarine exhalative origin and was absorbed from seaweater by clay minerals. Tourmaline was formed at an early stage of metamorphism up to staurolite grade. At higher metamorphic grades staurolite became unstable and porphyroblasts of cordierite and tourmaline were formed. The boron is suggested to be from the same brines which supplied tungsten for the extensive stratabound scheelite occurrences found in banded amphibolites and in some tourmalinites in the Malene supracrustal belt.

A Sm/1bNd isotopic study of heterogeneous granulites from the Archean Kasai-Lomami gabbro-norite and charnockite complex (Zaire, Africa)

Sm/1bNd model ages ( t DM ) of acid granulites from the Kasai Complex agree with previous Rb/1bSr and U/1bPb ages of ∼ 2.8 Ga for the early and main stage of granulite-facies metamorphism. These Sm/1bNd results give an upper limit of 3.1 Ga for the age of the protoliths of the charno-enderbites and metapelitic gneisses, which represent the majority of the acid rocks of the complex. A Sm/1bNd study (whole-rock and internal isochrons, and t DM ages) of the associated basic granulites (meta-gabbro-norite massif and metadolerite dykes crosscutting the acid granulites) demonstrates that the second stage of granulite metamorphism, corresponding to regional deformation of all the rocks, is nearly coeval with the emplacement of the basic rocks at ∼ 2.4 Ga.

Textures and c-axis orientations of deformed quartz crystals from porphyric dikes of the Alpine »Root Zone« (Western Alps)

Deformation textures and c-axis preferred orientations of quartz phenocrysts from porphyric dikes of the Alpine »Root Zone« have been formed under conditions of greenschist to low amphibolite facies. It is shown that the deformation textures as shear planes and kink bands, boudins, grain boundary sutures, subgrains, coarse and fine recrystallized grains, deformation lamellae and fractures are developed in a chronological sequence during first increasing and later decreasing temperatures. The c-axis orientations are chiefly influenced by kinking during the early stage of metamorphism and later by recrystallization but not by the initial orientations of the c-axes. The shape of crossed-girdles is related to the type of strain. At the beginning of polygonization during increasing temperatures basal-a glide as a dominant glide mechanism is replaced by prism-c glide and vice versa during decreasing temperatures. The average angular velocity of c-axes is 0.4‡ per 1 % flattening.

Garnet evolution in pre‐Variscan pelitic rocks from the Lake Emosson area, Aiguilles Rouges Massif, Western Alps

Abstract The chemical evolution of garnets from pelitic rocks of probable Palaeozoic age corresponds to a complex metamorphic evolution of the host rocks.Among the almandine‐rich garnets (Alm60–80), two main types of evolution can be distinguished. Early Mn‐rich garnets coexisting with kyanite may be replaced by plagioclase and then, during a late stage, by biotite and/or sillimanite. The second type of evolution corresponds to an overgrowth of Mn‐poor late‐stage garnet on older Mn‐rich garnets which corresponds to a thermal peak with sillimanite‐type of metamorphism. This new garnet may appear either as an overgrowth with a strong discontinuity, or as small, new euhedral garnet or as skeletal garnet.This chemical evolution of garnet corresponds to an early collisional stage of metamorphism (of high pressure type with high Mn values) of probable Ordovician age followed by uplift and a thermal peak (low Mn values) in Devonian times.

The development of the dendritic organization of primary and secondary motoneurons in the spinal cord of Xenopus laevis. An HRP study.

During embryonic and larval development of the clawed toad, Xenopus laevis, two different populations of motoneurons appear in the spinal cord. In this study the development of primary motoneurons which innervate the axial musculature (used during embryonic locomotion) and of secondary motoneurons which innervate the extremity musculature (used for locomotion during metamorphosis and thereafter) was analyzed with horseradish peroxidase (HRP) as a neuronal marker. After application of HRP to the axial musculature (rostral five postotic myotomes) the first labeled primary motoneurons were found at stage 24/25. During development gradually more labeled neurons were observed. These primary motoneurons send their dendrites into the marginal zone (white matter). At first only dorsal and lateral dendrites develop (stages 25-33), followed by ventral dendrites (stage 37/38). Up till stage 48 the developing dendrites extend throughout the marginal zone. Hereafter the marginal zone increases particularly at the dorsolateral edge, a development which is not followed by the dendrites of the primary motoneurons. The dendrites of mature primary motoneurons (stages 58-62) occupy the ventral and ventrolateral parts of the marginal zone. At stage 48, shortly after the hindlimb bud arises (stage 46, early metamorphosis), the first neurons related to this developing extremity could be labeled in the ventrolateral part of the lumbar spinal cord. At first these secondary motoneurons bear only a few dorsal dendrites of which only the tips reache out in the adjacent white matter. Already at stage 50 these dorsal dendrites have invaded the whole dorsolateral part of the marginal zone. Also the first ventral dendrites were observed at this stage. Later, at stage 53/54 also some ventral dendrites have reached the white matter together with a few lateral dendrites. At these early metamorphic stages already some primary afferent fibers were found making contact with the dorsomedial dendrites. At stage 58 for the first time recurrent axon collaterals were found, which extend into the ventromedial part of the marginal zone. The development of motoneurons in the spinal cord seems to be characterized by two phases: (1) establishment of contacts between motoneurons and target muscles, and (2) subsequent formation of connections of these motoneurons with other nerve cells within the central nervous system. The dendrites of primary motoneurons follow the development of the marginal zone, while dendrites of secondary motoneurons develop into an already well developed marginal zone.(ABSTRACT TRUNCATED AT 400 WORDS)

Oxygen isotope fractionation and disequilibrium displayed by some granulite facies rocks from the Fraser Range, Western Australia

The granulites of the Fraser Range are assumed to have formed in a carbon-rich fluid, and are generally devoid of hornblende, and lack obvious hydrous retrograde features. In these granulites, pyroxene, garnet, plagioclase and quartz are the minerals most likely to retain the oxygen isotope ratios fixed at an early stage of initial granulite metamorphism. Temperature estimates using these minerals commonly suggest that oxygen isotopic exchange ceased in the range 600 to 680°C. The peak metamorphic temperature was probably ∼ 850°C as based on the stability fields of the coexisting minerals and some cation temperatures from coexisting pyroxenes in these rocks. Ilmenite may be slightly out of isotopic equilibrium with the other minerals. Thus, grains of quartz, feldspar, pyroxene and ilmenite have suffered considerable oxygen isotopic exchange during the retrogressive phase of the metamorphism, in spite of the fact that very little water was present in these granulites. The observed deviation from the peak metamorphic temperatures can be explained by essentially closed system solid-state diffusion (on at least a scale of centimetres) during slow cooling of the rocks from ~850 to 650°C, followed by more rapid cooling down to ∼ 300°C. Such an explanation is not at variance with the radiometric data available for rocks from the area, which suggest that the latter phase could have involved uplift rates of ≳0.5 mm/yr for a period of about 40 Ma. Wholerock δ18O values on non-quartzose mafic granulites, about 7.2%., fall within the range of basalts affected by seafloor weathering.

Uranium and thorium in paleozoic basalts of Nova Scotia (Canada)

In the Paleozoic basalts of Nova Scotia (Canada) metamorphosed to a greenschist facies grade, U and Th are closely associated with immobile elements (e.g. Zr and Nb). The coherence of these elements with K, typical of igneous rocks is, however, absent, U and Th are apparently not affected by greenschist facies metamorphism as are alkali and alkali earth elements and their variation thus reflects primary magmatic processes. It seems that during the early stages of metamorphism, U and Th were retained together with several other incompatible elements (Zr, Nb, La and Ce) in stable secondary phases or alternatively these elements may be held in primary accessory minerals such as zircon and apatite.

Histochemical study of the amphibian digestive tract during normal and thyroxine‐induced metamorphosis. II. Acid phosphatase

AbstractThis histochemical study comprises a comprehensive overview of acid phosphatase distribution along the entire length of the digestive tract from esophagus through large intestine of growing and metamorphosing larvae and mature frogs of a single anuran species, Rana pipiens. The main site of enzyme localization throughout the length of the tube is the supranuclear area of the mucosal epithelium. However, activity of the enzyme varies markedly, not only in different locations (e.g., weak in the esophagus, strong in the small intestine), but also in different stages of larval development. During limb bud—early metamorphic stages (I—XX), activity is localized only in epithelial cells (supranuclear zone and scattered basal foci) and in glands of the stomach. Activity in these sites increases when remodeling of the digestive tract begins in the latter stages of this period. By mid‐metamorphosis (XXI—XXII), shortening of the tract has become maximal, and acid phosphatase‐positive epithelial cells have degenerated and sloughed into the lumen. In contrast, enzyme activity appears (albeit transitorily) in a new location, namely, in connective tissue thickening along the length of the tract. A similar histochemical picture can be induced precociously by thyroxine treatment. By the end of metamorphosis (XXIII—XXV), activity again appears in mucosal epithelium, but in newly differentiated adult‐type cells as well as in gastric and initially‐forming esophageal glands (the only two types of multicellular glands in the digestive tract). In adult frogs, activity remains in these sites and in scattered points (probably phagocytes) in the connective tissue; however, activity is generally weaker than in early‐stage larvae.

REE, Cs, Rb, Sr and Ba in glaucophane-bearing eclogites and associated rocks, Sunnfjord, Western Norway

A study of REE (La, Ce, Nd, Sm, Eu, Tb, Yb and Lu), Cs, Rb, Sr and Ba in eclogites, amphibolites and enclosing granitic gneisses in the Sunnfjord area, western Norway, shows that the central parts of the larger eclogitic bodies, having a thickness of ∼ 10 m, appear to have a fairly undisturbed igneous composition, while smaller bodies, having a thickness of ∼ ⩽ 5 m, and the margins of the larger ones were enriched in REE, Cs, Rb and Ba at a pre- or early-metamorphic stage. Post-eclogitic retrograde processes were accompanied by metasomatic introduction of alkalies, and Sr and Ba into the metabasites. The geochemical data are obtained by means of radiochemical neutron-activation analysis.

ORAL CHEMORECEPTOR ORGANS OF BULLFROG TADPOLES DURING METAMORPHOSIS.

Degeneration of the premetamorphic papillae and development of the fungiform papillae during metamorphosis of bullfrog tadpoles were investigated by electrophysiological and scanning electron microscopic methods. Premetamorphic papillae were observed during the early metamorphic stages, and these degenerated rapidly at about metamorphic stage 20. The anlage of the tongue appeared at about metamorphic stage 10, but the anlage of the fungiform papillae appeared at about metamorphic stage 18. The microvilli at the apex of the fungiform papillae were observed at about metamorphic stage 21. At metamorphic stage 24 the fungiform papillae had a similar structure to that of adult frogs. Taste responses were recorded from the glossopharyngeal nerve of the tadpole. The responses to 1 M sucrose and 0.01 M quinine hydrochloride could be observed at metamorphic stage 6 or later, though during stage 20 the responses were very weak. The response to 0.02 M ammonium chloride appeared at metamorphic stage 6, but disappeared at stage 20 and did not reappear later. These results indicate that the fungiform papillae become functional as chemo-receptor organs at about metamorphic stage 21 and that, before the fungiform papillae function, the premetamorphic papillae serve as chemoreceptor organs in the tadpole.

Thyroxine concentrations in blood serum and pericardial fluid of metamorphosing tadpoles and of adult frogs

Thyroxine (T 4) was measured by double antibody radioimmunoassay in blood serum and pericardial fluid of individual tadpoles and frogs of Rana catesbeiana. The pattern of change of mean T 4 values during tadpole growth and metamorphosis was similar in serum and pericardial fluid. In growing tadpoles, stages V–XVIII, all T 4 concentrations were below the limit of detection (<0.20 μg/dl). Mean T 4 values first became detectable in early metamorphic stages, XIX, XX; they reached a peak (0.94 μg/dl serum) at stages XXI, XXII, XXIII. Differences in mean values between these three stages were not significant. At the end of metamorphosis, stages XXIV, XXV, mean T 4 concentrations dropped to levels similar to those of stages XIX, XX. However, in adult summer frogs mean T 4 values for serum and pericardial fluid were somewhat higher than mean values at the end of metamorphosis. Despite this general developmental pattern, T 4 concentrations in some individual animals at each stage, including metamorphic stages, were below the limit of detection (<0.20 μg/dl).

A scanning and transmission electron microscope study of the premetamorphic papillae: possible chemoreceptive organs in the oral cavity of an anuran tadpole (Rana japonica).

Premetamorphic papillae of an anuran tadpole (Rana japonica) were studied by scanning and transmission electron microscopy. Premetamorphic papillae of several shapes are seen in and around the oral cavities of tadpoles during late larval and early metamorphic stages. These papillae are composed of three parts: the apical cellular part, the underlying connective tissue core and the epithelial covering. In the apical cellular part, two populations of cells are observed: apical and basal cells. The apical cell has a slender cytoplasmic process whose apical surface is exposed in the oral cavity. The basal cell is located at the basal portion of the apical cellular part of the papilla without researching the oral cavity. A long solitary microvillus and a bunch of short microvilli are seen on the apical surface of each apical cell. The apical cells contain dense-cored vesicles of 100 nm diameter and make synaptic contacts at their basal membranes with terminals of nerve fibers. Possible chemoreceptive function of the premetamorphic papilla is discussed.

HORMONES CONTROLLING COLLAGEN SYNTHESIS DURING METAMORPHOSIS IN THE THIGH BONE OF THE TADPOLE OF RANA CATESBEIANA.

The rate of 14 C-proline incorporation into collagen in the thigh bone of the Rana catesbeiana tadpole was determined in vitro. Intraperitoneal injection of bovine prolactin caused an increase in the rate of collagen synthesis during the premetamorphic stages (stages 12-16) and the early metamorphic stage (stage 18), but it exerted no effect on collagen synthesis in the metamorphic stages (stages 20-25). On the other hand, injection of growth hormone stimulated the rate of collagen synthesis in the metamorphic stages and caused a slight increase in the premetamorphic stages. When a tadpole in the early premetamorphic stages (stages 12-14) was kept in 5 × 10-8 M thyroxine solution for several days, the rate of collagen synthesis became higher than that in the bone of the control animal. The rate of collagen synthesis was not enhanced by prolactin in the thyroxine-treated tadpole, but was stimulated by growth hormone, even when the thyroxine-treated animal remained in the premetamorphic stages. With the treatment of the tadpole by thyroxine, prolactin-sensitivity seems to be reduced, and growth hormone-sensitivity becomes apparent.