ALBERT

Notes: Résumé 1o Le recensement des adultes et des nymphes dans la nature dePheidole pallidula montre que le pourcentage des soldats varie en cours d'année: faible à la sortie de l'hibernation, il s'élève progressivement et atteint son maximum à l'entrée de l'hiver. 2o Il est possible de reproduire ces variations au laboratoire, ce qui permet d'analyser les facteurs régulant l'apparition des soldats à la sortie de l'hibernation. a) L'âge des ouvrières par rapport à la sortie d'hibernation semble sans effets. En effet, des ouvrières sorties d'hibernation depuis plusieurs semaines et qui ont déjà élevé un couvain d'ouvrières ne sont pas plus aptes à l'élevage des soldats que celles sortant d'hibernation. b) Malgré une évolution saisonnière de leur taille, les œufs sont bipotentiels: les œufs de printemps et les œufs d'éte sont susceptibles de donner naissance à des soldatset à des ouvrières. Même les œufs des reines fondatrices peuvent évoluer en larves de soldats. L'orientation dépend des soins donnés aux larves et non d'un facteur blastogénique. c) L'abondance des ouvrières nourrices, favorise l'éclosion des soldats en plus grand nombre. d) Toujours à la sortie de l'hibernation, la production des soldats est inhibée lorsque le pourcentage des soldats adultes est supérieur à environ 4% même si il y a plusieurs milliers d'ouvrières nourrices. Dès lors, on peut expliquer l'absence ou le faible nombre de soldats dans le premier couvain produit au printemps: les colonies possèdent plus de 5% de soldats adultes, d'où inhibition de l'élevage de nouveaux soldats au profit de la production d'ouvrières; l'éclosion de ces dernières fait chuter le pourcentage des soldats, ce qui lève l'inhibition. De plus, le pourcentage des soldats en dessus duquel il y a inhibition s'élève au cours de la saison, permettant alors l'accumulation des soldats nouveau-nés.

Notes: Zusammenfassung Erstmals wurde ein Symposium über die Technologie und über die Haltungsmethoden für Bienenvölker in Flugräumen abgehalten. Wie die Berichte aus mehreren Laboratorien zeigten, wird heute allgemein die neue Technologie angewandt, dievan Praagh (1972) publieziert hat. Es wird über beträchtliche Erfolge berichtet: Haltung von tropischenApis-Arten (A. dorsata undA. florea) über einen Zeitraum von mehr als einem Jahr in einem Flugraum in Europa. Ueberwinterung empfindlicher Rassen und Mutanten in Gebieten mit kaltem Klima. Haltung von Königinnen nach der instrumentellen Besamung in Kleinstvölkchen bis zum Zeitpunkt der Eiablage. Dennoch erreichen die Bedingungen im Flugraum hinsichtlich des biologischen Effektes nicht das Niveau der Haltung im Freien (kein Anwachsen der Volksstärke über ein bestimmtes Maß, keine Anregung zur Schwarmtendenz, keine Aufzucht von Drohnen). Die möglichen Ursachen für diese Erscheinungen und Wege zu einer Verbesserung wurden diskutiert.

Notes: Abstract We discuss the inversion of stress drops from seismic observations on the basis of crack or stress-drop models of earthquake mechanism. Since a formal inverse problem cannot be posed at present we discuss implications of solutions to direct problems. We first discuss the static approximations used to obtain stress drop from seismic moment and source dimensions. We show that the geometrical effects are quite significant if only one source dimension has been retrieved from seismic observations. The effect of variable stress drop is discussed and we show that the inverted stress drop is not a simple average of the actual stress drops on the fault. We discuss the energy release during faulting and show that the apparent stress has a complicated relation to the stress drop on the fault. We also show that the static stress drops obtained by seismologists are a lower bound to the actual dynamic stress drops on the fault. This may in part explain disagreements with laboratory results. Finally, we discuss the inversion of source dimensions from the far-field radiation. We analyse two extreme, simple dynamical source models, a circular fault and a rectangular fault and show that geometry has a much more pronounced effect on radiation than is usually acknowledged.

Notes: Abstract The magnitude of shear stress in the lithosphere is bounded from below by the apparent stress and stress drop during intraplate earthquakes. Apparent stresses and stress drops for a number of mid-plate earthquakes are calculated from the earthquake magnitude, SH wave amplitude spectra, and estimates of the length of the fault zone. Apparent stresses vary between 0.1 and 2 bars, ifm b is used as a measure of seismic energy, and stress drops lie between 2 and 70 bars. There is no systematic difference in either apparent stress or stress drop between these intraplate events and typical plate boundary earthquakes. These bounds on intraplate shear stresses are consistent with the inference from current models of plate tectonic driving forces that regional stress differences in the plates are typically on the order of 100 bars. The highest stress drops measured for midplate earthquakes under this model represent nearly total release of local tectonic stress.

Notes: Summary The general problem of determining the figure of the earth leads to the solution of the geodetic boundary value problem. By its discrete approximation we obtain ‘the discrete disturbing potential’ that maintains all properties of the original problem. Thus, the discrete approximation of the disturbing potential can be used in studying the behaviour of the earth's gravity field outside the disturbing masses. The deflections of the vertical are one of the quantities describing the behaviour of the earth's gravity field. A method for their computation from the discrete solution of the geodetic boundary value problem is put forth and estimates for its accuracy are given.

Notes: Abstract The arrival at the Yellowknife Array (YKA) of closely-spaced P-waves having slightly different values ofdT/dΔ, azimuth, and amplitude has been simulated using synthetic 1 Hz wavelets. Adaptive-processing determinations of apparent slowness and azimuth show a remarkable pattern of fluctuations with time for varying separations of the interfering pulses. In the critical separation range 0.30 to 0.55 s, these fluctuations greatly exceed the differences in arrival vectors of the primary wavelets themselves. Observation of characteristic interference patterns on real array seismograms might permit the identification of triplications associated with radial velocity anomalies in the lower mantle. Processed YKA seismograms for three events at distances close to 90° are presented, which, despite apparently simple P onsets illustrate the pattern of drift indT/dΔ expected for such a triplication.

Notes: Summary Mean travel-time residuals of P waves for the period 1964–1970 at stations in North America and Europe are well separated into large domains of positive and negative values. The spatial distribution of residuals in North America is in good agreement with the structure of the upper mantle obtained from Rayleigh wave dispersion and is in accord with magnitude anomalies and heat flow data. A systematic variation of residuals in time is found to be sensitive to major changes in the nature of the earthquake source distribution, as for example aftershocks, as well as to changes in methods of detection of first arrivals. Residuals at neighboring stations are correlated up to distances of the order of 2°. Half year mean residuals at stations within 2° distance from the epicenters of strong earthquakes have a sudden jump 1.5 years before the occurrence of an earthquake. A formal algorithm based on this pattern permits prediction of the times of all 16 earthquakes with magnitudeM≥7.5 occurring during the interval 1966–1972. Although the average duration of the alarm periods is about half the total time interval of the catalog, so that the algorithm has no practical importance, these results are statistically significant on a 99% level of confidence.

Notes: Summary Himalayan muscovites from pegmatites of Kathmandu Valley, Nepal yield an age of 2–23 m. y. by fission track (f.t.) method. The uranium concentration is estimated to be 10−10 atom/atom.

Notes: Summary In 1974 and 1975 deep seismic sounding experiments were carried out in the area of the Betic Cordillera in southern Spain. A network of crustal seismic profiles was established with shotpoints at sea close to Cádiz, Adra and Cartagena and on land at Alquife near Guadix. The lengths of the profiles range from 50 km near Alquife to 440 km for the main profile between Cádiz and Cartagena parallel to the strike of the Betic Cordillera. The main profile was supplemented by a reversed recording line close to the Mediterranean coast between Adra and Cartagena and another one perpendicular to the main tectonic strike from Adra towards the north. The first interpretation of the data indicates considerable variation in the crustal thickness. A preliminary inversion leads to a three-layered model of the crust. The mean compressional velocity is about 5.1 km/s down to a depth of 4 km. Below this the velocity is 6.13 km/s from 4 to 16 km where it increases to 7.14 km/s. TheP n-velocity is 8.18 km/s. The crust-mantle boundary is reached at a depth of 27 km near Cartagena and lies 32 km deep near Adra, Underneath the gravity minimum of the Betic Cordillera the crust-mantle boundary is found at a depth of about 36 km. Below the Betic zone a pronounced zone of low velocity with 7.7 km/s seems to exist in the depth range from 40 to 60 km.

Notes: Summary A new computation method is described which determines the focal coordinates, theP n-andP G-velocity, the focal time and the Moho-depth in the case of near earthquakes. The method is provided especially for areas where the crustal parameters are insufficiently known. It presumes that the standard error ofP n-andP G-arrival times is a minimum. The problem turns out to represent the solution of a set of at least seven equations with seven unknown parameters. Four of these unknowns can be separated in advance. This leads to a considerable simplification. The three remaining unknowns are the focal coordinates. Their best fitting values are found by the gradient method. An example is presented which shows how errors can arise if the initial trial coordinate is chosen at an unfavourable position.

Notes: Abstract Using simulated data, it is demonstrated that one may estimate the body wave velocity in the crust by measuring the angle of incidence ofP-waves provided only the very first part of the signal is used. This angle has been measured for a set ofP-waves at the NORSAR long period instrument sites. Combining these observations with measurements of apparent velocities, we find that the data indicates a crust velocity of 6.1±0.4 km/sec. While it is somewhat uncertain to what depth the value is representative, the observations are in obvious disagreement with previous authors who concluded that long periodP-waves were not affected by the earth's crust. Because of difficulties in separating the effects of real velocity variations from measurement errors, the details of the observedP-wave variation across the array are difficult to interpret. The consistent behavior of the data does, however, indicate that variations of approximately 3% must exist in the crustalP-wave velocity across the array.

Notes: Abstract Linear mesospheric circulation models can quite realistically simulate mid-latitude mesospheric circulation and structure. In doing so they provide estimates for dissipation (Rayleigh friction ∼2×10−6s−1) and vertical mixing (≤30 m2s−1) appropriate near the mesopause.

Notes: Abstract The coalescence of water drops of sizes comparable to rain drops (200–2500 μm diameter) was investigated. The method used provided a good separation between collision and coalescence effects. The result suggests a dependence of the coalescence efficiency on both the size of the large drop and the ratio of the radii of the interacting drops (p-ratio). The coalescence was observed to rapidly decrease due to bouncing and partial coalescence as the angle of impact increased from head-on to grazing angle. However, some bouncing was observed at very low impact angles. The results of the coalescence efficiency were fitted with an empirical equation for use in numerical models of cloud growth and precipitation development.

Notes: Abstract An attempt is made to use the barotropic vorticity equation in spectral form in order to study barotropic instability when the basic current has east-west quasi-stationary asymmetries on the scale of long waves. This is done by expressing the spectral equations in three different ways. In the first experiment a 9-component system is integrated and the long waves are allowed to propagate freely. In the second experiment the long waves are constrained to propagate slowly and in the third experiment, they are removed altogether. The motivation behind the present investigation is due to observations made in the motion fields of the tropics. These are characterized by quasi-stationary long waves and very energetically active and propagating short waves. The presence of quasi-stationary long waves seems to enhance the energy exchanges between the short waves and the mean zonal current and also allow for larger energy values for the short waves. Long term integration (90 days) shows a 6-day mode in thev time spectra at latitude 10°N and a 15-day mode in theu time spectra at individual grid points in the equatorial latitudes. Any possible connection between this peak and the observed peak of 15 days in the completely different physics of ‘Kelvin waves’ is left as a conjecture.

Notes: Abstract The standard deviations and time-spectra of small ion number density have been measured at ground level under different atmospheric stability conditions. The auto-correlation correlograms and the time-spectra imply a scale of fluctuations corresponding to 1 to 4 min. No clear relationships between standard deviations of small ion number density and micro-meteorological parameters are observed. Thus the results are not a support for Monin-Obukhov similarity theory. For the highest frequencies the slopes of the spectra seem to follow the −5/3-law fairly well and the frequencies of the peak values of individual spectra lnfS(f) increase when the atmosphere stability increases, which is valid for ordinary micrometeorological parameters.

Notes: Abstract This model concerns the analysis of Aurora initiated travelling pressure waves in an isothermal atmosphere. Electro-dynamic Lorentz Force associated with auroral electric current density during the periods of geomagnetic activity is invoked as a possible exciting source. The dispersion phenomena in auroral induced acoustic gravity modes in the earth's atmosphere are examined and various cut-off frequencies analysed. Finally, an attempt is made to obtain a far field representation of the forced oscillations by means of Green's Function technique. Therefrom, the spectral amplitudes of the ground-level oscillations are computed. Incorporating various scaling factors, it is deduced that these amplitude components are in reasonable agreement with the results of recent measurements.

Notes: Abstract In steady state condition, non-linear laminar flow of fluid into a well partially penetrating a porous aquifer of finite thickness is considered. The influence of such a flow on discharge and its dependence on related physical quantities are investigated. It is observed that the discharge into the well decreases as the depth of the well is decreased and the region of non-linear laminar flow is widened, which is quite obvious from physical considerations. As a particular case, result for a fully penetrating well has been deduced.

Notes: Summary An attempt has been made to interpret the striking difference, in focal properties, between the intermediate and shallow earthquakes in Central Greece and an observed time sequence of these shocks by a lithospheric model. This model consists of a lithospheric slab descending from the Ionian to the Aegean and a back-arc expanding Aegean lithosphere. Thrust faulting near the top surface of the slab, caused by the sinking of the slab, triggers spreading and normal faulting in the back-arc Aegean region.

Notes: Abstract Mean bulk densities of various samples of dry atmospheric aerosol particles sampled at different sites and during different seasons and weather situations range between 1.8 and more than 3 gm cm3.

Notes: Abstract The dependency on relative humidity of the settling velocity of aerosol particles in stagnant air and of the diffusion coefficient due to Brownian motion of aerosol particles was computed for six aerosol types and different particles sizes in dry state. The computations are based (1) on mean bulk densities of dry aerosol particles obtained from measurements or from the knowledge of the chemical composition of the particles, (2) on micro-balance measurements of the water uptake per unit mass of dry aerosol substance versus water activity at thermodynamic equilibrium, and (3) on measurements of the equilibrium water activity of aqueous sea salt solutions. The results show a significant dependence of the settling velocity and Brownian diffusion of aerosol particles on relative humidity and on the particle's chemical composition.

Notes: Abstract A numerical evaluation of the complete Navier-Stokes equations of motion for steady-state, incompressible flow past an infinite circular cylinder is given in terms of the stream function, vorticity, and pressure distribution past such bodies. A method is described which allows use of these flow characteristics: (1) to approximate the characteristics of air flow past hexagonal columnar ice crystals falling under gravity at terminal velocity in air, (2) to compute the trajectory of supercooled cloud drops relative to such ice crystals, and (3) to determine the efficiency with which short columnar ice crystals and needle shaped ice crystals collide with supercooled cloud drops. It is found that for all columnar type ice crystals riming is negligible if the cloud drop size is less than 5∼ μm, and that for riming to commence short columnar crystals must have diameters larger than ∼50 μm, while needle crystals must have diameters larger than ∼40 μm. It is further shown that the collision efficiency cut-offs at the small drop radius and at the large drop radius end of the collision efficiency diagram can be explained on the basis of the cloud drop trajectories for these drop size ranges.

Notes: Abstract The characteristics of the disturbances in the atmosphere and oceans and in other stably stratified and rotating fluids are analyzed according to their phase and group velocities. It is shown that both stable stratification and rotation augment the velocity of the sound waves, and that the internal gravity waves and inertial waves are mutually exclusive when the Brunt-Väisälä frequency is different from the Coriolis parameter. It is also shown that both the barotropic and the internal Rossby waves are well separated from the gravity waves and that they can be represented accurately by the quasi-geostrophic potential vorticity equation, even close to the equator, except for the one member withn=0 which is coupled with an eastward propagating gravity wave.

Notes: Summary Transverse fragmentation of the egg ofDrosophila melanogaster results in the formation of partial larvae. Anterior and posterior egg fragments develop the respective partial larval patterns. The partial patterns do not add up to the complete pattern. Fragmentation near the middle of the egg during early cleavage causes a gap of 3–4 segments on average in the larva. This gap is reduced to 2 segments on average if operations are performed at the early syncytial blastoderm stage. Fragmentation near the pole regions from early cleavage stages onwards causes a gap of only 2 larval segments on average. When the egg is fragmented at the columnar cellular blastoderm stage or later, the gap at all positions amounts to the size of one segment or less. A gap is also found after incomplete fragmentation, when the ooplasmic bridge between both egg parts was constricted beyond a certain limit. A specific shift of the segment-forming capacities along the egg axis is observed from syncytial blastoderm stages onwards. After partial longitudinal fragmentation no additional structures are observed. In general, the partial transverse patterns add up to the complete pattern, but minor structures like single denticles are missing near the fragmentation site. The results are discussed with respect to current concepts of segment pattern formation during early embryogenesis in dipterans.

Notes: Summary Abnormal denticle belt patterns can occasionally be observed in abdominal belts of partial larvae obtained from egg fragments. The abdominal belts have the following features in common: 1) The number of denticles of an abdominal denticle belt may increase, depending on the space occupied by a distinct segment or the whole body region. The arrangement of the denticles in such enlarged belts is less regular than in normal belts. 2) Enlarged denticle belts are also found in the terminal segment of a fragment, or in the segment next to it when the larval pattern is interrupted by fragmentation. The denticle belt in the adjacent segment(s) may then be supressed. 3) All denticles in a belt (or part of a belt) are orientated posteriorly if the distance to the posteriorly adjacent belt (or part of a belt) is larger than normal, or if this denticle belt is suppressed. Conditions anterior to a segment do not seem to exert any influence on denticle orientation.

Notes: Summary The concentration of RNA synthesised in the prolonged interphase of micromeres at the 16 cell stage is about 9 times higher per unit volume than in the other blastomeres. Since there are cytoplasmic connections between micromeres and macromeres, a transfer of the micromere RNA by simple diffusion is to be expected.

Notes: Summary Two genetic operations have been combined in order to ascertain whether there are differential proliferation rates in the syncytial nuclei and the blastoderm cells prior to the formation of the imaginal disc anlagen. Early chromosome loss caused by the mutantca nd has been associated with the generation ofMinute (M/M +) genotypes in normal (M +/M +) zygotes or of non-Minute genotypes inMinute zygotes. The results indicate that there is no growth competition betweenMinute and non-Minute cells prior to the formation of the imaginal discs. Growth competition, however, leads later, during the proliferation phase of the discs, to the demarcation of compartment boundaries within imaginal discs.

Notes: Summary Isolated amphibian (Triturus alpestris) gastrula ectoderm was treated with cyclic nucleotides for 24 h and cultured up to 12 days. Explants treated with$cyclic N6-Monobutyryl-adenosine-3′∶5′-monophosphate, cyclic Dibutyryladenosine-3′∶5′-monophosphate and cyclic Dibutyrylguanosine-3′∶5′-monophosphate in a concentration of 10−3 and 10−5 M did not differentiate into mesoderm- or endoderm-derived tissues. The number of explants with small neural and neuroid structures did not exceed the percentage found in the control series. Inductions could also not be obtained when ectoderm was dissociated prior to the treatment with cyclic nucleotides, or when theophylline (which inhibits phosphodiesterase) was added to the culture medium. The results are discussed with regard to the possible mode of action of the vegetalizing factor.

Notes: Summary Electrophoretic separation of hemoglobins of normalXenopus laevis and of isogenic animals derived from female hybrids ofXenopus laevis×Xenopus gilli revealed 5–9 components in premetamorphic larvae, and 3–4 components in adult toads. InXenopus laevis the number of larval hemoglobin components showed considerable variation, but this variation was absent in isogenic tadpoles, suggesting a genetic basis for hemoglobin polymorphism in larvae. Electrophoretic separation of larval and adult hemoglobins at different concentrations of acrylamide and treatment of these solutions with mercaptoethanol revealed that larval hemoglobin components are charge isomers, whereas adult hemoglobin was found to contain a minor dimeric component. Estimation of hemoglobin components showed that the main increase in adult hemoglobin, i.e from 30–90% of total hemoglobin, occurs within 4 weeks after completion of metamorphosis. By incroporation of3H amino acids in vivo a switch to preferential synthesis of adult hemoglobin and a corresponding decrease in larval hemoglobin production could be demonstrated during early climax stages. This suggests that thyroid hormones are involved in the hemoglobin transition. Yet chemical inhibition of the larval thyroid by thiourea resulted in a delayed but complete hemoglobin transition without morphological transformation. It is concluded that hemoglobin transition and morphological transformation of theXenopus tadpole require different concentrations of thyroid hormones.

Notes: Summary 1. Histological analyses were made of imaginal discs and histoblasts during the larval development ofDrosophila melanogaster to determine the number of cells, the patterns of cell division and the growth dynamics in these adult primordia. Histological studies were also made of the imaginal rings which are the primordia of the adult salivary gland, fore-and hindgut, the anlage cells of the midgut and several larval and embryonic tissues. 2. In the newly-hatched larva, the immature eye-antenna, wing, haltere, leg and genital discs contain about 70, 38, 20, 36–45 and 64 cells respectively. These numbers include cells destined to form cuticular elements as well as peripodial, tracheal and nerve cells and probably the progenitors of adepithelial cells. The number of cells counted in the various imaginal disc anlagen is 1.5 to 4 times higher than the numbers deduced from genetic mosaic analyses by other investigators and reasons for these differences are given. 3. About 12 h after fertilization, mitosis ceases in all tissues of the embryo except the nervous system. After the larva hatches, mitosis resumes in most of the imaginal anlagen and in some larval tissues. The time of resumption of mitosis in the imaginal anlagen was determined after treating the larvae with colchicine for 2 h. 4. Among the imaginal discs, the eye disc is the first to begin cell division, at about 13–15 h after the hatching of the larva (first instar) followed by the wing (15–17 h), the haltere (18–20 h), the antenna, leg, and genitalia (24–26 h, early second instar), and finally the labial and dorsal prothoracic discs (52–54 h, early third instar). The cell doubling time for various discs was calculated from cell counts and the times agree closely with the doubling times deduced from clonal analyses by other workers: e.g., 7.5 h for the cells of the wing disc. 5. The imaginal ring of the hindgut first shows cell division early in the second instar. The imaginal rings of the foregut and salivary glands, the anlage cells of the midgut and the cells of the segmental lateral tracheal branches begin to divide early in the third instar. 6. The histoblasts which are the anlagen of the integument of the adult abdomen do not increase in number from the time of larval hatching until about 5 h after pupation when they begin to divide. Their behaviour contrasts with that of the histoblasts of the other dipterans such asCalliphora, Musca andDacus, which begin to divide during the second instar. 7. The histoblasts are an integral part of the larval abdominal epidermis and, unlike imaginal disc cells, secrete cuticle during larval life. Each hemisegment consists of an anterior dorsal, a posterior dorsal, and a ventral histoblast nest containing about 13, 6 and 12 cells respectively. The 62 histoblasts in each larval segment represent about 7–8% of the total number of cells that form the integument of that segment. 8. The number of cells in a particular type of histoblast nest was constant for both male and female larvae and among the different abdominal segments, except that the anterior dorsal group of the first and the seventh segments contains fewer cells than those of the other segments. Although the male and female adultDrosophila lack the first abdominal sternite and the male lacks the seventh abdominal tergite and sternite, the ventral histoblast nests of the first and the dorsal and ventral nests of the seventh abdominal segments are present in the larval stages as well as in the prepupa and have the same morphology and cell number as similar nests in the rest of the abdominal segments. 9. The cells of the imaginal discs increase in volume about six-fold and their nuclei increase in volume three-fold between the time of hatching and the initiation of mitosis. The histoblasts increase in volume about 60-fold and their nuclei increase in volume about 25-fold between larval hatching and pupariation. 10. Prior to each cell division, the nuclei of the columnar cells of the disc epithelium and of the histoblasts appear to migrate toward the apical surface of the epithelium. The cells round up and shift toward the apical region where mitosis occurs. After cytokinesis, the daughter cells move back to deeper positions in the epithelium. Because the nuclei of the non-dividing cells continue to lie deep in the epithelium, this intermitotic migration of nuclei gives these epithelia a pseudostratified appearance. 11. Analyses of the growth of larval cells and of organs confirmed the observations of earlier investigators that cell division occurs only in a few larval tissues, whereas growth in the rest of the larval tissues is by cell enlargement and polyteny. During larval life, cell division was detected only in the central nervous system, gonads, prothoracic glands, lymph glands and haemocytes. Each tissue began mitosis at a characteristic stage in larval life. The larval cells that did not divide, grew enormously, e.g., epidermal cells increased in volume 150-fold and their nuclei increased in volume 80-fold. 12. The adepithelial cells, which give rise to some of the imaginal muscles, were first identified between the thick side of the imaginal dise epithelium and the basement membrane at the beginning of the third larval instar (50–52 h). The origin of these precursors of mesodermal structures was analysed and evidence is presented that the adepithelial cells come from the disc epithelium. The question of the origin of the mesoderm of cyclorrhaphan Diptera is reviewed and it is suggested that the imaginal disc ectoderm may become segregated from the rest of the embryo before gastrulation has occurred, that is before the mesoderm has been established.

Notes: Summary The development of the telotrophic ovary in the Staphylinid beetle,Creophilus maxillosus was examined. Cells, termed chordoblasts were identified in the germarium of 1-day-old pupae. Each of the chordoblasts undergoes a series of synchronous mitoses. Owing to the precise control of the cleavage plane, which is vertical to the long axis of the ovariole, each of the chordoblasts gives rise to a linear chain of sibling chordocytes. Extra DNA synthesis within each sibling string is usually limited to the most posterior chordocyte only, this being an oocyte progenitor. Divisions of the oocyte progenitor are differential mitoses in which the extra DNA material is transported preferentially towards the posterior pole of the spindle. As extra DNA synthesis and preferential segregation of this material result in gradual increase of this DNA in the nuclei of oocyte progenitors, cytokinesis of these cells becomes highly unequal, the larger of the two cells produced at each differential mitosis being as a rule the posterior cell, i.e. the oocyte progenitor of the next cell generation. As a resul of the series of differential mitoses each chordoblast gives rise to a number of nurse cells and only one definitive oocyte. It is suggested that somatic prefollicular tissue plays a decisive role in oocyte determination in the Coleopteran telotrophic ovary.

Notes: Summary Vegetalising factor was isolated from swimbladder of crusian carp (Carassius auratus) by solubilishing with 8 M urea the precipitate obtained after digesting the swimbladder with collagenase. The urea-soluble fraction vegetalised isolated presumptive ectoderm ofTriturus gastrula and produced both undifferentiated mesodermal and endodermal cells. Brief heating of the fraction changed its capacity to produce organised mesodermal tissues, such as notochord and somite, and the frequency of induction of undifferentiated cells was reduced. By inserting the urea-soluble fraction into the blastocoel of an early gastrula, embryos without epidermis were obtained. Some of the embryos consisted of undifferentiated mesodermal and endodermal cells, but in the remaining ones small fragments of notochord, small numbers of somites and pronephros developed, enclosed by endodermal cells.

Notes: Summary 1. The sensitivity to X-rays of 5 differentDrosophila cell lines has been studied. Statistical analysis of experimental data for doses between 10,000 and 16,000 roentgen showed that, for each cell line, the probability of survial of each cell is independent. According to the relationship observed between the dose and the survival frequency, the five lines studied can be classified into 3 groups. Moreover, the cell population of each line is heterogeneous with respect to radiosensitivity, some cells being more radioresistant than others. 2. UnirradiatedDrosophila cells seeded at a very low multiplicity are unable to multiply unless they are cultured among heavily irradiated cells. Each cell has an independant probability of initiating a clone. This probability,p, is different for each one of the 3 cell lines examined:p 1=0.69,p 3=0.35,p 6=0.02. These differences are likely to have a genetic origin. 3. The ability of a single cell to initiate a clone, when cultured among cells whose multiplication has been stopped by X ray irradiation, provides a simple and efficient cloning method. The conditions in which a given cell line could be cloned were defined after determination of the dose-survival relationship and estimation ofp. The cloning procedure is described. The homogeneity of the karyotype and cell morphology can be used to monitor the homogeneity of the cell population.

Notes: Summary Mouse embryos were collected at the 2-cell stage, cultured in vitro in the presence of3H deoxyuridine or uridine for 6 or 4 h and autoradiographed. Deoxyuridine is actively incorporated into the DNA of cleaving mouse embryos indicating the existence of thymidylate synthetase activity at least at the 4-cell stage and presumably already before this. RNAase treatment of embryos squashed on slides shows a weak but obvious incorporation of uridine into DNA of cleaving mouse embryos, from the 4-cell stage onwards; this incorporation is totally inhibited by hydroxyurea. The reduction of ribonucleotides to deoxyribonucleotides is a metabolic pathway already required for cleavage, as shown by hydroxyurea experiments. The second polar pody, known to incorporate thymidine, is unable to incorporate either deoxyuridine or uridine.

Notes: Summary The generalogical relationships of photoreceptor cells within the compound eye ofDrosophila have been studied using cell labelling, with either3H-thymidine or recessive mutations, during the third larval stage. It has been found that photoreceptor and secondary pigment cells arise from different precursor cells. Under the present experimental conditions, precursors of receptor cells give rise to about 8 elements which differentiate as R cells of two different groups. One of the cells differentiates as R7 and the remaining as any one of the R1 to R6. The last cells behave initially as equivalent, and can differentiate within the same or within different, but neighbouring, ommatidia. The class of R1 to R6 cell in which each one of these elements differentiates, seems to depend on the time of its origin. The implications of these findings for the formation of the ommatidial pattern are discussed.

Notes: Summary The 4 animal and 4 vegetal blastomeres of the eight-cell-stage ofTriturus alpestris were isolated and cultured for up to 12 days. Because of the difficulty of obtaining intact animal and vegetal blastomeres of the same embryo, we either cut off the vegetal blastomeres or sucked off the animal blastomeres. The culture of early embryonic amphibian cells is improved by the use of 50% Leibovitz-medium with added fetal calf serum providing a stable pH and optimal osmotic pressure. Isolated animal blastomeres differentiated to irregularly shaped ciliated epidermis. 30% of the cases showed small amounts of myotomes, notochord and neuroid cells in addition to irregular epidermis. The vegetal blastomeres formed trunk and tail structures but only 6% of all cases formed nearly complete head structures in addition. From the results we conclude that the vegetal blastomeres as well as the animal blastomeres of the eight-cell-stage are already determined as to their future fate. The possibility of partial regulation and the influence of asymmetric or irregular cleavage on the further development of isolated blastomeres is discussed.

Notes: Summary The problem of the regional specification of snout vibrissae and dorsal pelage hairs has been analysed in mouse embryos. Reconstituted homo-and heterotopic skin explants, consisting of epidermis and dermis from both regions, were cultured on the chorioallantoic membrane of the chick embryo. Recombinants of 12.5-day upper lip dermis and 12.5-day dorsal epidermis developed a small number of large vibrissal type follicles arranged in a recognizable rectangular vibrissal pattern. The reverse combinations of 12.5- or 14.5-day dorsal dermis and 11- to 12.5-day upper lip epidermis formed a single population of numerous and small follicles arranged in a typical pelage hair pattern (trio groups) or gave rise to a mixed population of follicles with both whiskers and pelage hairs. It is concluded that the dermis is responsible for the regional specification of the cutaneous appendages and their distribution pattern. However, at the time it was isolated, the upper lip epidermis already possesses the information for the morphogenesis of vibrissae, but remains malleable and responsive to the dermal influence.

Notes: Summary Parathion, administered before incubation or at the beginning of development (48 h) induces specific axial deformities which occur between 4 and 5 days in the chick and after 5 days of incubation in the quail. Morphological studies indicate that the teratogenic effects are first represented by myotome compressions, notochordal and neural tube distortions. The abnormalities develop quickly in the chick embryo but take place gradually in the quail embryo. In the two species, somites and primitive vertebrae undergo a normal differentiation and the perinotochordal cells differentiate into chondroblast like in the normal way. But later, the chondrogenesis extends to the intervertebral clefts and gives rise to the formation of an unsegmented vertebral column. In the quail, vertebral fusions are encountered in regions where no torsion occurs. Cervical malformations can develop in quail and chick embryo, when parathion is injected at late stages (2nd and 3rd thirds of the embryonic life). The axial deformities are morphologically similar to those observed after early treatment. But, vertebral fusions are rarer the later the embryos are treated. In chick embryos of 16 days' incubation, the cervical scoliosis occurs 5 h after the treatment. The rapid occurrence of the malformation and the results obtained after early treatment support the hypothesis advanced earlier that the disturbed morphogenesis is caused — in great part — by an abnormal physiology and/or differentiation of the muscles (Meiniel, Lutz-Ostertag et Lutz, 1969).

Notes: Summary The temporal pattern of cleavage in the egg of the axolotl,Ambystoma mexicanum, was studied 1. by time-lapse microcinematography, and 2. by counting the total number of blastomeres dissociated at successive stages. Eggs were filmed from the one-cell stage till the early gastrula either (A) simultaneously from above and below with a “double-camera” assembly, or (B) from the side with a single camera. The animal blastomeres divide synchronously from the 2nd up to and including the 10th cleavage. The cycle length is roughly constant from the 3rd till the 10th cleavage. The cycle from the 2nd to the 3rd cleavage is slightly longer, while that from the 1st to the 2nd cleavage is about 20% longer. After the 10th cleavage the synchrony of divisions is lost owing to variable lengthening of cell cycles in individual blastomeres. Gastrulation starts around the onset of the 15th cleavage in the animal blastomeres. The analysis of films taken in side view reveals seven recurring “cleavage waves”, from the 5th till the 11th cleavage. Cells in the animal, equatorial and vegetative regions in sequence repeatedly pass through the three successive phases of the cleavage cycle—rounding-up, division, and relaxation—but with a shift in phase. The start of the 10th cleavage division of the slowest vegetative cells more or less coincides with that of the 11th division of the animal cells; from then on the cleavage waves become increasingly obscured. Morulae and blastulae were dissociated by placing them in 1/15 M phosphate buffer (pH 7.8) for the duration of 2–3 cleavage cycles and then removing the vitelline membrane. In this solution cell divisions continued without disturbance of the temporal cleavage pattern. The dissociated cells were fixed either just prior to the onset of the next cleavage (up to the 10th cleavage) or at those times when cleavageswould have been expected, had there been no lenthening of cleavage cycles (beyond the 10th cleavage). The total cell number was counted, dividing cells being scored as two. Prior to the 11th cleavage the total cell number increased exponentially. Beyond the 10th cleavage the rate of increase was considerably lower. At the time when gastrulation would have started if the egg had not been dissociated, the total cell counts were 13,000–15,000, whereas the number anticipated without lengthening of cleavage cycles would be of the order of 130,000 (217). The application of Balfour's rule to amphibian eggs is criticized.

Notes: Summary Transplantations into the blastocoel of gastrulae and cultures in vitro of the stomodeal region ofPleurodeles waltlii Michah embryos have been carried out. These experiments gave the following results: Neural crest cells reach the stomodeal region at the young tail-bud stage (stage 22), and are able to take part in formation of teeth and cartilage, it is possible to dissociate the phenomena of mouth opening, complete mouth formation and complete head formation, differentiation of a digestive tube from the pharyngeal endoderm and the formation of a mouth opening both depend on the presence of mesentoderm and mesectoderm in the explant or in the environment, during the tail-bud stage a symmetry factor plays a part in mouth formation, bone formation likewise coincides with the presence of neural crest cells.

Notes: Summary Wing discs of the Indian meal moth may be cultured for extended periods in vitro. The discs produced a tanned cuticle after continuous incubation with β-ecdysone in medium conditioned with fat body or after a 24-h pulse incubation with β-ecdysone in plain medium. We investigated the ultrastructure of the cuticle deposited by such discs. We found that the treatment that produced the most complete cuticle in vitro was the 24-h pulse of hormone. We observed that cuticle formation in vitro was not “all-or-none.” Depending on culture conditions, discs produced cuticulin only, complete epicuticle, epicuticle plus diffuse endocuticle, epicuticle plus lamellate endocuticle, or even multiple layers of cuticle. The ultrastructural evidence suggests that continuous incubation with β-ecdysone in plain medium does not always inhibit cuticle formationper se, but does prevent tanning of the partially formed cuticle.

Notes: Summary Deficient limb buds composed of prospective stylopod and autopod are able to regulate the missing intercalary zeugopod, the origin of which was investigated by heterospecific quail/chick recombinants. The associations of quail prospective autopod and chick prospective stylopod failed to regulate. The reverse combination of chick prospective autopod grafted onto a quail prospective stylopod gave rise to a three-segmented limb. In 13 out of 16 cases the regulated zeugopod was made up of both chick and quail cells. Chick cells were located predominantly along the postaxial half of the zeugopod, while the quail cells made up most of its preaxial half. In two cases, the intercalary zeugopod consisted exclusively of chick cells originating from the tip and in one case of quail cells originating from the base. These results demonstrate that during the regulative processes, the prospective values of some of the original stylopodial and autopodial cells have been shifted along the proximo-distal axis, towards the expression of more distal as well as of more proximal structures. Heteropolar stylo-autopodial or zeugo-autopodial recombinants, in which the proximo-distal axis of the base was reversed with respect to that of the tip, were unable to regulate the pattern defects and thus revealed the importance of concordant p-d polarity for regulative processes to take place between abutted tissues.

Notes: Summary A mutant ofHydra attenuata is analysed, theaberrant, which is distinct from the wild type in having a smaller head with fewer tentacles and only half the number of head-specific cells. The rate of head and foot regeneration and the doubling time are slower inaberrants than in normal hydra. The lower head-forming potential is paralleled by a reduced concentration of head-specific morphogens: compared to the wild type, in theaberrant the concentration of head activator is reduced to 70% in the head and to 50% in the body, the concentration of head inhibitor is reduced to 50% in the head and to 80% in the body. Theaberrant is more sensitive (3 times) to added head activator and less sensitive (〉5 times) to added head inhibitor than the wild type. The slower rate of foot regeneration is paralleled by a lower content of foot-specific morphogens: compared to the wild type, in theaberrant the foot activator is reduced to 40% and the foot inhibitor to 70%.

Notes: Summary The unfertilized egg ofArtemia salina is not covered with any extracellular structure. No special organelles are found in the sub-cortical plasma. From the moment of fertilization, a membrane is progressively secreted by the egg. The membranogenous substance is first seen as large granules in the smooth endoplasmic reticulum, presumably transformed within Golgi elements and extruded in vesicles liberated from the Golgi apparatus. Retained by a glycocoat or by contact with the fluid of the genital tract, it spreads out into a fertilization membrane, soon surrounding a perivitelline space. The process lasts till 1 1/2 h after fertilization.

Notes: Summary 1. The developmental potentials of the four quadrants of the male foreleg disc ofDrosophila melanogaster were analysed by culturing excised quadrants for 3 days and 10 days in adult hosts prior to metamorphosis. 2. The cultured pieces underwent different types of pattern regulation in a circular direction. The upper medial piece was able to regenerate the missing structures of the disc, thus confirming the findings of earlier reports. The three remaining pieces could undergo pattern duplication in mirror-image symmetry. The lower medial piece revealed in addition a slight capacity for regeneration from the vertical cut surface. 3. The duplicating pieces differed markedly in their frequencies of pattern duplication: duplications occurred with very high frequencies in lower medial pieces, with intermediate frequencies in upper lateral pieces, and with very low frequencies in lower lateral pieces. 4. Both lower lateral and upper lateral pieces underwent a progressive loss of most markers with increasing culture time. 5. Claws were regenerated solely by upper medial pieces. 6. Transdetermined structures, too, were encountered only in upper medial pieces. 7. The results are discussed with respect to the two major current models of pattern regulation in imaginal discs, the “gradient model” and the “clock model”. 8. It is suggested that the differences in the frequencies of pattern duplication reflect the unequal spacing of circular positional values within the three duplicating quadrants. Under this assumption the data indicate a progressive decrease in the density of circular positional values with increasing distance from the upper medial quadrant of the disc.

Notes: Summary 1. The egg ofPollicipes polymerus, the common intertidal gooseneck barnacle, has been studied by electron microscopy. Constriction rings, similar to the contractile rings of cleaving cells and polar lobes, move unidirectionally from the animal to the vegetal pole of newly fertilized eggs. This is referred to as peristaltic constriction. The present paper describes the fine structure of the egg during first polar body formation and peristalsis. 2. During formation of the polar body, dense bodies are produced by the Golgi and extracellular plaques are observed. Thin microfilaments (40–60 Å) are in the egg adjacent to the polar body. 3. In eggs undergoing peristalsis, the appearance of extracellular spheres, flocculent material and filaments is observed. Intracellularly large numbers of multivesiculate bodies, glycogen granules, mitochondria and protein-carbohydrate and lipid yolk bodies are seen at the level of constriction. 4. Thin microfilaments are found in the cortical area of newly-fertilized eggs exclusively in peristaltic constriction rings. Filaments are oriented primarily in a meshwork, although circumferentially-oriented filaments are also found in rings near the vegetal pole. Microvilli extend into the space created between a constriction and the elevated egg membrane. 5. A model is proposed to explain the peristalsis in this species. It is suggested that information from a pacemaker region activates peristalsis by affecting filament polymerization and orientation. One function of peristalsis may be elongation of the egg from a sphere to an ovoid, although other possibilities such as elevation of the egg membrane, segregation of the lipid yolk to the vegetal pole and predetermination of the first cleavage plane are also discussed.

Notes: Summary In the imaginal discs ofMusca domestica, Drosophila melanogaster, D. simulans, D. hydei, andZaprionus spec. the enzyme aldehyde oxidase (AO) appeared in a clear-cut pattern. In the leg and eye-antennal discs of these species this pattern shows a high degree of conformity, while that of the wing and haltere discs is species-specific. No aldehyde oxidase activity was detected in the imaginal discs ofCalliphora erythrocephala, Phormia regina orLucilia cuprina, but the discs of these species are characterized by grossly similar patterns of 5′-nucleotidase. Since the other species studied lack this enzyme, the two enzymes may perform similar functions in the morphogenesis of the discs. The coincidence of the sharp boundary of the AO pattern in the leg and wing discs ofD. melanogaster with the boundary between the anterior and posterior disc compartments gives a strong indication for the existence of analogous compartments in other discs showing a similar sharply bounded AO pattern. Compartmentalization may be considered a general phenomenon which occurs in discs of all segments and is not restricted toD. melanogaster. From the changes in the AO pattern during disc development it can be deduced that the localisation of this enzyme is regulated by supracellular determination involving positional information.

Notes: Summary Buds ofCassiopeia andromeda have been transected into fragments of various sizes. Depending on their original position in the organism, on their size and on the age of the dissected buds, the fragments either regenerated or developed to a solitary polyp's head without stalk and peduncle. Generally, basal fragments tended to regenerate complete buds, young apical parts mostly differenciated polyp heads whereas apical and middle parts of progressively older buds regenerated buds with increasing frequency. To explain the alteration of the developmental capacities a head inhibitor is postulated which originates from the basal end of the buds and which expands towards the apical pole with increasing age of the buds.

Notes: Summary The hormonal control of evagination of the imaginal leg discs of the fleshflySarcophaga crassipalpis was studied by means of ectopic transplantation of discs from mature larvae or prepupae onto prepupal hosts. Evagination was influenced by the age of the donor and the developmental commitment of the host. Discs from non-diapuse as well as diapause-committed donors did not differ in their capacity to evaginate and differentiate. Mature larval discs from either type of donor could evaginate only when transplanted onto non-diapause hosts; they failed to evaginate on diapause-committed hosts even though host discs evaginated in situ about 40 h after transplantation. Discs from white prepupae evaginated whether transplanted onto non-diapause or onto diapause-committed hosts.

Notes: Summary Changes in the intestinal wall ofAlytes obstetricans (Amphibia, Anura) were quantified during thyroxine treatment. The relative proportion of each intestinal wall component was determined in tissue sections. Autoradiographic studies on intestine with3H-thymidine revealed the distribution and frequency of labeled nuclei. The labeling index in the primary epithelium falls to zero by 3 days. Thyroxine treatment induces a decrease in the growth rate of this tissue, just before its degeneration and complete elimination by 14 days. Three days after T4-treatment, a secondary epithelium develops from basal stem cells. Its labeling index rises to a maximum of about 50% by 9 days, and thereafter declines. Cell proliferation is less marked in the extraepithelial zone, which nevertheless thickens during this thyroxine-induced metamorphosis.

Notes: Summary Mitotic recombination was induced, by X-irradiation at the blastoderm stage, in flies heterozygous for one of the temperature-sensitive paralytic mutationsshibire andtp-2. The results show that these mutations can be used to detect the presence of clones in the central nervous system through the temperature-sensitive paralysis of individual legs. Mitotic recombination can also be used to examine the effects of these mutations in the peripheral nervous system; shibire is thus shown to affect the function of sensory neurons.

Notes: Summary Minis have a doubling time of 2.4 days,maxis of 8 days.Minis regenerate head and foot 5 h faster thanmaxis.Minis have fewer tentacles (4.6) per head thanmaxis (6.1). Inmini the concentration of the head activator is equal to that inHydraattenuata, but the concentration of the head inhibitor is reduced (2-fold in the head, 1.2-fold in the body). The concentrations of the foot factors are normal.Minis respond likeHydra attenuata to head activator, foot activator and foot inhibitor, but they are less sensitive to head inhibitor Inmaxi the concentration of the head activator is higher than inmini (5-fold in the head, 10-fold in the body) and that of the head inhibitor is also higher (4-fold in the head, 5-fold in the body). The concentration of the foot inhibitor is normal, that of the foot activator is doubled.Maxis are insensitive to added head activator and less sensitive to added head inhibitor and foot inhibitor. Their response to foot activator is normal.

Notes: Summary 1. Eggs of the midgeSmittia were investigated by light microscopy and transmission electron microscopy. This paper describes elements and architecture of periplasm and yolk endoplasm before the formation of pole cells. 2. The periplasm is coated externally by the oolemma and a multilayered egg shell. The periplasm consists of a cytoplasmic matrix rich in ribosomes; it contains mitochondria and ER cisternae, some annulate lamellae and an occasional Golgi complex. Microtubuli were demonstrated only rarely. Accumulations of a dense granulated substance resembling in its structure the oosome material were frequently observed. 3. The yolk endoplasm is a cytoplasmic network embodying proteid yolk particles, lipid droplets and accumulations of glycogen. The endoplasm is continuous with the periplasm and shows the same cell constituents. It may form between 3 and 7 cytoplasmic islands free of yolk particles. Rosette-shaped membranous structures in the yolk endoplasm are interpreted as nuclear envelope organizing centres. 4. Three carefully analysed eggs contained 2 nuclei each. both nuclei were situated in the posterior egg half. 5. Periplasm and yolk endoplasm are characterized by random distribution of cell elements. No zonation or special accumulations could be recognized. 6. The spatial distribution of the egg components studied did not indicate that any of these components could function as a determinant in embryonic pattern formation.

Notes: Summary The developmental accretion of up to nine individual gangliosides in foetal brains, peri- and postnatal cortices, postnatal cerebelli and olfactory lobes and in the liver and the spleen were investigated in mice and compared with that of glycoprotein-bound sialic acid and the activity of the acetylcholinesterase. In foetal brain and in postnatal liver and spleen more sialic acid was found bound to glycoproteins than to gangliosides. In postnatal brain structures, however, ganglioside-NeuAc predominated and increased between the 7th and 21st d about 2-fold in the olfactory lobes and cerebellum and more than 3-fold in the cortex. During foetal development the relative quantities (mol %) as well as the absolute concentrations (compared with the fresh weight) of GM1, GM2 and GM3 in the brain decreased, whereas those of GD1a, GD1b and GQ increased. This pattern change continued perinatally in the cortex up to the end of the first week. Thereafter the pattern changed little, but the concentration of all gangliosides present increased much more rapidly, especially between the 10th and 13th d. The postnatal cerebellum and olfactory lobes contained higher concentrations of GM1 and GM3 than the cortex, both gangliosides decreasing in favour of their di-, tri- and tetrasialo-homologues during the third postnatal week. In all brains structures the accretion of GD1a and GT1 was proportional to the increase in the activity of the acetylcholinesterase. Unlike the brain structures, the ganglioside pattern in the liver and spleen, characterised by a predominance of monosialogangliosides and of GD3, did not change noticeably during the first three weeks after birth. The coincidence of the changes in ganglioside accretion observed in the different brain structures with successive periods of morphological differentiation further support the suggestion that gangliosides may play an important role in control of the growth and differentiation of developing nerve cells.

Notes: Summary 1. The development of the adult shell field inLymnaea stagnalis can be followed from its embryonic origin through the shell gland stage. The shell gland represents the most important stage in the differentiation of the entire organ. At no time do the invaginated cells take part in the elaboration of the periostracum. This is solely the function of the rosette, i.e. of the noninvaginated cells. At this stage the shell field is already definitively differentiated into zones. 2. Prior to the shell gland stage, cell division and incorporation of not yet differentiated ectoderm cells are responsible for the growth of the shell field. The shell gland, and later the shell field, grows exclusively by means of mitotic cell division. 3. The formation of the free mantle edge begins when a portion of the elongated edge cells of the shell field arches upward. At the same time and outside of this circular ridge a second ring of undifferentiated ectoderm cells is produced. The two ridges become raised and apposed to one another, thereby creating the periostracal groove between them. They grow jointly from the body of the animal to form the free mantle. 4. One after the other, from the outside to the inside, the zones of the shell gland become functionally active. Accordingly the initial pellicle of the shell takes the form of a ring and consists of membrane-like lamellae. Later it becomes underlain by the other layers of the periostracum (1–3). Since the areas which give rise to the respective layers move away from the shell gland pore during subsequent growth of the shell field, these layers can be absent in the middle of the pellicle. The initial central hole in the shell sometimes becomes occluded only by the innermost shell layers. 5. When secretion begins, the cells are already morphologically differentiated and possess the same appearance as that of their mitotic descendents in the corresponding zones of the mature shell field. 6. The secretion of periostracum material proceeds via elimination of vesicles through the apical cell membrane. Only zone 2 has developed special membrane invaginations for the purpose. 7. In the flat-celled area of the shell field organically bound calcium appears to be transported in the form of granules through the cell interstices.

Notes: Summary Films of cleaving embryos of the axolotl,Ambystoma mexicanum, taken by the “double camera” technique, were used in order to arrive at a more detailed staging based on quantitative criteria. Drawings were made of the animal hemispheres just prior to the start of each cleavage cycle from the 6th to the 15th cleavage. The number of cells intersected either by the (apparent) “egg diameter” (up to the 10th cleavage) or by “half the diameter” (from the 10th cleavage onwards) was determined. The cell numbers for each cleavage cycle did not overlap with those of the previous or succeeding cycles. On the basis of these cell numbers, in place of the four Harrison stages 6–9, 10 successive stages were established each of which corresponds to one cleavage cycle.

Notes: Summary Daughterless is a temperature-sensitive, maternal effect mutation ofDrosophila melanogaster. Homozygousdaughterless females raised at temperatures above 22°C do not produce any female progeny. It was possible to rescue these female embryos by injecting cytoplasm from non-mutant unfertilized eggs into embryos fromdaughterless mothers. Cytoplasm from unfertilized eggs laid by homozygousdaughterless mothers was ineffective. Surprisingly, the cytoplasm from developing embryos with either wild-type ordaughterless mothers could also effect rescue. Based upon this data, we suggest that male and female embryos ofdaughterless mothers differ in their ability to initiate the synthesis of a product during the nuclear multiplication (cleavage) stage of embroniic development in the absence of a putativeda + maternally-synthesized factor, and that this is the basis for the sex-specific action of theda maternal effect.

Notes: Summary Cessation of gluconeogenesis during oocyte maturation inMisgurnus fossilis L. is accompanied by an increase of pyruvate dehydrogenase activity (EC 1.2.4.1). The activity of other enzymes of citrate and pyruvate metabolism (citrate synthetase, EC 4.1.3.7, pyruvate carboxylase, EC 6.4.1.1., malate dehydrogenase, EC 1.1.1.37) remains constant during oocyte maturation and early embryogenesis. In the course of oocyte maturation the levels of acetyl-CoA, pyruvate and citrate remained unchanged, but the level of malate and oxaloacetate underwent drastic increase. The level of phosphoenolpyruvate increased about two-fold. The mitochondrial (NAD+)/(NADH) ratio was calculated by measurement of intermediates of the glutamate dehydrogenase reaction and it was found to increase six-fold during oocyte maturation. The lower mitochondrial (NAD+)/(NADH) ratio in oocytes compared to that in the embryos is likely to be responsible for the transfer of reducing equivalents from mitochondria to cytoplasm, while in embryos transfer in the opposite direction takes place.

Notes: Summary The derivatives of 110 mosaic genital discs of gynandromorphs have been analysed microscopically. It has been found that theanalia of both sexes are homologous and derive from a single primordium (see Fig. 1a). Whether male or female anal plates are formed depends on the genetic constitution of the cells. This is analogous to the development of male sex combs versus female transversal rows on the forelegs of gynandromorphs. In contrast, the data for thegenitalia (see Fig. 1 b) are best explained if it is assumed that there are two genital primordia in everyDrosophila embryo: a male primordium that will only develop into genitalia if populated by XY (or XO) nuclei, and a female primordium that will only do so if populated by XX nuclei. This model, as depicted in Figure 2, is compatible with all our gynandromorph data and also with observations onMusca andCalliphora where in fact two separate genital primordia are found.

Notes: Summary We describe the range of phenotypes caused by cell death when larvae of the heat-sensitive cell-lethal mutant,l(1)ts726 ofDrosophila, are subjected to heat treatment at different stages of development. When the treatment extends into the pupal period, certain bristles fail to develop but the disc derivatives are otherwise normal. Earlier treatments cause the replacement of sets of leg and eye-antennal markers by mirror image duplications of neighbouring sets. The results are compared in detail with those expected under a gradient model proposed earlier to account for the phenotype. It is found that although the results for the second leg are in excellent agreement with the predictions of the model, a more elaborate hypothesis is necessary to account for the eye-antennal disc data. Abnormal head patterns fall into several distinct categories, any one of which could be explained by postulating the existence of a gradient, if other categories did not also occur. The markers affected in each case belong to overlapping sets, and each category of pattern can be induced by heat treatments administered throughout the temperature-sensitive period. The statistical distribution of the data is such that only one category of pattern would be detected in a small scale experiment. The possible implications relative to pattern formation in normal development are discussed.

Notes: Summary Isolated nuclei ofPhysarum contain endogenous RNA polymerase activity. We provide evidence for four different states of RNA polymerase B: 1. free enzyme (85%); 2. weakly bound enzyme (10%) and 3. tightly bound enzyme (0–4%), which can be solubilized from isolated nuclei with 0.5 M and 1.5 M NaCl respectively; 4. “initiated” enzyme. The latter fraction (1–5% of the total RNA polymerase B) is not soluble in salt extractions, does not accept external templates, shows high salt optimum for transcription (0.4 M NaCl) and produces by elongation RNA molecules of mainly 10 S. Treatment of isolated nuclei from differentiating cultures with Triton X-100 increases the proportion of the “initiated” enzyme at the expense of the tightly bound enzyme fraction. This indicates a potential transcription control mechanism which operates at the chromatin level and results in variable proportions of silent and transcribing RNA polymerase B molecules during differentiation of Physarum.

Notes: Summary The origin and evolution of the embryonic gonad ofViviparus viviparus were studied ultrastructurally. The gonad is formed by migration and multiplication of pericardial cells. There are several successive stages during gonad organogenesis: during the sexually undifferentiated stage with one cellular type, the gonad is made up of primordial cells which seem to be identical. The sexually undifferentiated stage with two cell types is characterized by the differentiation of germinal and non-germinal cells. The non-germinal cells are linked to one another by septate junctions and their long extensions completely surround the germinal cells which remain isolated and do not form junctions with their neighbours. The gonad sexualisation does not appear until after organogenesis, towards the end of embryonic development, or even after birth.

Notes: Summary Cauterization of pole cells in embryos of the Colorado beetle does not prevent organogenesis of the gonads. So, pole cells do not govern to the differentiation of the gonadal mesoderm (this latter is limited to abdominal segments 6, 7 and 8). Moreover, this mesoderm develops into testis or ovary even without any innitial germ cells.

Notes: Summary Non-budding mutants ofChlorohydra viridissima regenerate heads 6 h faster thanHydra attenuata and the number of tentacles per head is higher. The polarity in pieces from the gastric region is the more labile, the smaller the pieces are. In regenerates heads and tentacles form much more frequently than feet, giving rise to bipolar or multiheaded structures. Buds very seldom form under normal conditions, but they occasionally occur in regenerating animals with two cut surfaces. The higher head-forming potential in the mutant is paralleled by a higher head-activator concentration (20-fold in head, 4-fold in body), than inHydra attenuata, which is not accompanied by an equivalent increase in head-inhibitor concentration (1.4-fold in head, 2-fold in body). The foot-activator concentration is slightly reduced (1.3-fold), the foot-inhibitor concentration is higher (1.6-fold) than inH. attenuata. The mutant is extremely insensitive to head activator, relatively insensitive to head inhibitor and foot inhibitor, but sensitive to foot activator.

Notes: Summary The mutationbicaudal (Bull, 1966) causes embryos to develop a longitudinal mirror image duplication of the posteriormost abdominal segments, while head and thorax are missing. These embryos occur with varying frequencies among eggs laid by mutant females, irrespective of the paternal genotype. Recombination and deletion mapping indicate thatbicaudal (bic) is a recessive, hypomorphic, maternal-effect mutation mapping at a single locus on the second chromosome ofDrosophila melanogaster close tovg (67.0±0.1). The frequency of bicaudal embryos depends on the age of the mother, her genetic constitution and the temperature at which she is raised. Best producers are very young females hemizygous forbic (bic/Df(2)vg B ) at 28° C. Under these conditions 80% to 90% of the eggs which differentiate can show the bicaudal embryo phenotype. Upon ageing of the mother the frequency of bicaudal embryos declines rapidly, and most of the eggs develop the normal body pattern. Temperature shift experiments suggest a temperature-sensitive period at the onset of vitellogenesis. The mutation causes several types of abnormalities in the segment pattern of theDrosophila embryo, which are interpreted as various degrees of expression of the mutant character. The most frequent abnormal phenotype is the symmetrical bicaudal embryo with one to five abdominal segments duplicated. Less frequent are asymmetrical types, in which the smaller number of segments is always in the anterior reversed part. Other phenotypes are embryos with missing or rudimentary heads, and embryos with irregular gaps in the segment pattern. In bicaudal embryos, the pole cells, formed at the posterior pole of the egg prior to blastoderm formation, are not duplicated at the anterior. The significance of thebicaudal phenotypes for embryonic pattern-formation inDrosophila is discussed.

Notes: Summary 1. The foraging activity ofParavespula vulgaris (Linn.) was studied in the field by means of an entrance-exit apparatus placed over the burrows of underground nests. 2. Departing foragers carried earth loads or no loads. Incoming foragers were either pulp, flesh, full or partial liquid carriers or carried no load. Some incoming foragers carried mixed loads. 3. The mean fresh and dry weights of pulp, flesh, earth, full and partial liquid loads and the fresh weights of the crop liquid of pulp, flesh and earth carriers were determined. 4. No correlations were found between worker size and flesh or pulp loads but significant correlations were found between worker size and earth and liquid loads.

Notes: Résumé Une étude démographique des sociétés deMyrmica rubra L. fut menée durant deux ans afin de préciser l'âge des individus. Un nid est récolté chaque mois (tableau I). Les pourcentages de nymphes, d'imagos et d'ouvrières présentant 5 degrés successifs de pigmentation cuticulaire (Cammaerts-Tricot, 1974a) sont déterminés (fig. 2). Un examen biométrique du couvain (fig. 3) et de certaines ouvrières (tableau II) complète et confirme nos premières observations. De juin à novembre, deux séries plus ou moins superposées d'ouvrières se succèdent. Les individus de ces deux séries diffèrent par leur taille: les ouvrières nées en début de saison, à partir de larves ayant hiverné, sont grandes; les fourmis apparues en début de saison, à partir de larves issues d'œufs pondus en juin, sont plus petites. On peut donc suivre l'acquisition progressive du degré de pigmentation ultime dans deux lots parallèles et plus ou moins distincts d'ouvrières. Cette évolution dure deux ans et s'effectue surtout pendant la bonne saison (fig. 4). Précisons qu'aucun hiatus n'existe entre les deux séries signalées d'ouvrières: la ponte, les développements larvaires et les nymphoses se déroulent de manière continue, mais avec deux maxima distincts, de juin à novembre. Enfin, les dates exactes auxquelles les changements démographiques, ont lieu dépendent sans doute des conditions climatiques, ce qui rendrait compte des divergences mineures relevées entre nos observations et celles d'autres auteurs (Brian, 1951;Petal, 1972) (fig. 4).

Notes: Zusammenfassung Wenn Kundschafter vonHarpagoxenus sublaevis ein Nest ihrer SklavenartLeptothorax acervorum (Fabr.) oderL. muscorum (Nyl.) entdeckt haben, rekrutieren sie andereHarpagoxenus-Arbeiterinnen aus ihrem Muttervolk zum Raubzug mittels Tandemlauf in derselben Weise, wie dies vonMöglich et al. (1947) fürLeplothorax-Arbeiterinnen beschrieben wurde, die Nestgenossen zu Futterquellen führen. Im Mutternest zeigt eine rekrutierende Ameise ein charakterisches Aufforderungsverhalten: Sie läuft unter Schüttelbewegungen rasch umher, betrommelt mit Antennen und Vorderbeinen die Köpfe und Fühler von Nestgenossen und sterzelt dann vor dem Nesteingang mit erhobener Gaster und ausgestrecktem Stachel, bis eine andere Ameise sie berührt und ihr im Tandem folgt. Verliert eine Führerin während des Tandemlaufs ihre Folgerin, hält sie sofort an, sterzelt und lockt sie mittels Giftdrüsensekret wieder herbei. Hat das Tandem den Eingang desLeptothorax-Nests erreicht, bricht die führende Ameise den Tandemlauf oft dadurch ab, daß sie sich umwendet und das folgende Tier kurz mit den Antennen betastet. Die Führerin kehrt dann meist zurück um weitere Nestgenossen zu rekrutieren, während die Folgerin gegen Wirtsarbeiterinnen zu kämpfen beginnt, wenn diese aus ihrem Nest hervorkommen. Die beim Tandemlauf eingesetzten chemischen und taktilen Signale scheinen beiHarpagoxenus sublaevis und seinen SklavenartenLeptothorax acervorum undL. muscorum dieselben zu ein. Wir konnten häufig gemischte Tandems beobachten, meist mit einerHarpagoxenus♀ als Führerin, aber in anderem Zusammenhang auch mit einerLeptothorax♀ als Führerin und einerHarpagoxenus als Folgerin.

Notes: Summary Studies of polyethism in workers ofNasutitermes exitiosus showed that the oldest instar (LW5) of the large worker line carried out most of the immediate repairs following a breach to the mound surface. LW4 workers participated minimally, and younger instars of both the large and the small worker lines took no obvious part. On the other hand, all worker instars, including the youngest, were prominently represented in foraging parties. Comparisons ofN. exitiosus andN. costalis are made.

Notes: Summary Most mounds of the myrmicine antSolenopsis invicta in the area of Tallahassee (Florida, U.S.A.), were found to be oval in shape with the long axis of the mound oriented in a north-south direction. This «magnetic» orientation is of probable thermoregulatory significance and is comparable to mound orientation phenomena found in the ant subfamily Formicinac and in the termites.

Notes: Résumé Au cours du développement post-embryonnaire des sexués normaux deCubitermes fungifaber, il s'établit un dimorphisme sexuel, visible par l'allongement progressif du 7e sternite chez la femelle, corrélatif à la formation de la chambre génitale. Au cours de mues nymphales, les gonades et les tractus génitaux se développent de façon synchrone et régulière. L'ovaire, qui se compose d'un très grand nombre d'ovarioles, dès le premier stade nymphal, se différencied'arrière en avant très progressivement; dans le testicule la spermatogenèse se déroule de façon progressive. On peut noter que chez la femelle la position des divers débouchés est intersegmentaire: gonopore, entre les 7e et 8e sternites; débouché de la spermathèque, entre les 8e et 9e sternites; débouché des glandes collétériales, entre les 9e et 10e sternites. A la mue imaginale, il se produit une forte différenciation de l'appareil génital; chez la femelle, la chambre génitale s'achève par la formation du pli intersternal et l'apparition de sensilles et les annexes acquièrent une structure glandulaire; chez le mâle, des aires de stockage du sperme (vésicules séminales?) se différencient dans les portions distales des canaux déférents et le pénis (avec des sensilles) se constitue. La maturité sexuelle paraît acquise chez le mâle, alors que chez la femelle elle semble se faire plus tard, chez l'adulte. Tous ces faits soulignent le contraste entre les sexués et les neutres dont l'appareil génital est bloqué au premier stade larvaire.

Notes: Summary Alcoholic queen bee extracts (Apis mellifera L.) were administered toK. flavicollis pseudergates and nymphs. In comparison with the control groups the treated groups had more moults into supplementary reproductives and fewer moults into white soldiers; the treated queens laid fewer eggs. There are evidences that the queen bee extracts acted mainly on theK. flavicollis reproductives reducing their ability both to inhibit the differentiation of supplementary reproductives and to stimulate the differentiation of soldiers, and reducing the queens' fertility.

Notes: Résumé Nous proposons une méthode mathématique basée sur les équations différentielles non linéaires et le concept d'ordre par fluctuations, visant à la simulation du comportement collectif des sociétés d'insectes. L'exemple traité, les premières phases de la construction du nid chez les termites, montre l'intérêt qu'une telle formulation présente. Les points essentiels que nous retiendrons sont: 1o Connaissant les mécanismes d'interaction entre les éléments du système ou moyennant une série d'hypothèses sur ceux-ci, il est possible de formuler un système d'équations différentielles dont l'étude va nous donner une image du comportement collectif du groupe. 2o Outre les innovations introduites dans le système, les fluctuations de ses éléments (concentrations d'individus, d'odeurs, de matériaux...) constituent un des moteurs essentiels de la structuration des systèmes. Ce point semble être en parfait accord avec les observations expérimentales, qui montrent le rôle que jouent les éléments fluctuants d'une colonie.

Notes: Zusammenfassung Die Haemolymphe frisch geschlüpfter Imagines enthält noch kein Vitellogenin. Junge Arbeiterinnen und Königinnen sind daher als infertil einzustufen. Die Vitellogenin-Synthese setzt erst bei über 5 Tage alten Bienen ein. Sie führt zu einem raschen Anstieg des Vitellogenin-Titers und leitet die subfertile Phase ein. Gegen Ende der zweiten Imaginal-Woche geht diese in die fertile Phase über, die durch eine starke Zunahme der Ovargröße gekennzeichnet ist. Bei den physogastrich werdenden Königinnen steigt mit zunehmender Legeleistung das Körpergewicht stark an. Die Arbeiterinnen legen nur eine geringe Zahl von Eiern, zumeist Nähreiern. In der 4. Woche setzt bereits wieder eine Ovardegeneration ein. Der Vitellogenin-Titer sinkt während der nun folgenden langen postfertilen Phase langsam ab. Bis zum Alter von 40 Tagen verschwindet Vitellogenin völlig aus der Haemolymphe. Damit ist erneut ein infertiler Zustand erreicht, der während der restlichen Lebensdauer der Arbeiterinnen beibehalten wird. Diese Fertilitätsphasen werden von allen Arbeiterinnen im weiselrichtigen Meliponen-Volk durchlaufen. Vitellogenin-Titer und Entwicklungsgrad der Ovarien sind dabei positiv korreliert. Für die Ausbildung von Nähreiern ist ein hoher Vitellogenin-Titer Voraussetzung. Das elektrophoretische Muster der Haemolymph-Proteine von stachellosen Bienen und Honigbienen stimmt noch weitgehend überein, ebenso die Ontogenese der imaginalen Fertilitäts-Änderungen. Sie vollziehen sich bei den Meliponen-Arbeiterinnen entsprechend ihrer längeren Lebensdauer allerdings erheblich langsamer als bei Honigbienen. Diskutiert werden entwicklungsphysiologische Aspekte der Produktion heteromorpher Eier bei Meliponen und Vorstellungen über die hormonelle und pheromonale Kontrolle der Fertilität sowie über die Evolution der fortpflanzungsphysiologischen Kastendifferenzierung bei Bienen.

Notes: Summary The volatile secretions produced by the labial gland in male bumble-bees,Bombus Latr., belonging to the subgenusPyrobombus D. T., have been studied in six species:B. cingulatus Wahlb.,B. hypnorum L.,B. jonellus K.,B. pratorum L.,B. lapponicus Fabr. andB. scandinavicus Friese. Totally, 181 specimens have been analyzed. The secretions, which are used for marking different objects along the flight-route, have been analyzed by capillary gas chromatography and combined capillary gas chromatography/mass spectrometry. Isoprenoids and fatty acid derivates together make up the secretions. The former group of compounds dominates the marking secretions from the species studied, with the exception ofB. scandinavicus. The compositions of the secretions are characteristic for each species.

Notes: Summary Some Japanese species ofCeratina bees exhibit habits which seem to be precursors to social life, namely: 1) Removal of larval feces by the mother, accompanied by destruction and reconstruction of cell partitions. 2) Transport of immatures within nest. 3) Guarding by the mother at the nest entrance, which is effective in protecting the immatures from parasites. 4) Association of the mother and juvenile adults in autumn, with pollen intake by juveniles from the mother, and 5) Prolonged life span of some females, followed by brood rearing in the second year. Three nests ofC. japonica and four ofC. iwatai, each containing two or more females in brood rearing condition are recorded. The relations among co-habiting females are variable: semisocial, delayedly eusocial,eosocial (nom. nov.) and quasisocial. The significance of these findings are discussed in connection with social evolution and various social types found or assumed in Hymenoptera.

Notes: Zusammenfassung An weisellosen Sozietäten der PharaoameiseMonomorium Pharaonis L. (Formicidae, Myrmicinae) wurde der Mechanismus der Kastendeterminierung untersucht. Die Aufzuchtergebnisse zeigen, daß mindestens zwei Faktoren an der Ausbildung der Morphen beteiligt sind: 1. eintrophogener Faktor, der wahrscheinlich gleichzusetzen ist mit einer Aenderung der Nahrungsversorgung der Brut in physiologisch oder tatsächlich weisellosen Sozietäten, 2. einblastogener Faktor, die Entwicklungspotenz der Eier: Eier begatteter Weibchen, älter als 4 Wochen, entwickeln sich in weisellosen Sozietäten zum Teil zu Geschlechtstieren (Weibchenund Männchen). Entsprechend entwickeln sich Eier unbegatteter Weibchen gleichen Alters zu Männchen (diese Brut geht in weiselrichtigen Kolonien zugrunde). Eiser begatteter Jungweibchen entwickeln sich auch unter günstigsten Bedingungen nur zuMicrergaten, während die Eier unbegatteter Jungweibchen stets im Laufe der Larvalentwicklung absterben. Die unterschiedliche Entwicklungspotenz der Eier manifestiert sich in variierender Eigröße: mit zunehmendem Alter der legenden Weibchen ist sowohl für diploide als auch für haploide Eier eine Abnahme desEivolumens feststellbar. Der Zusammenhang zwischen funktionellen Lebensstadien der Weibschen, Weibchenernährung und dem Mechanismus der Kastendeterminierung wird in seiner Bedeutung für die polygyne Sozietät diskutiert.

Notes: Abstract Continuous measurements of ultrasonic pulse transit times over 10 m baselines between fixed points in each of three mutually perpendicular directions are made routinely in solid rock. The most significant current experiment is in a large underground support pillar (30 m×30 m×200 m high) 700 m below ground level in an active mine. Velocity measurements to a precision of 2 parts in 106 allow stress changes of order 1 kPa to be monitored, and compared with simultaneous strain measurements (for which a capacitance strain sensor is used) to examine the mechanisms of large scale stress relief processes. Characteristic stress relief cycles (of magnitude 200–3000 kPa) are found to migrate through the pillar as impressed loads are accommodated by the rock mass.

Notes: Summary In this study, values of the Ångström turbidity coefficient (β) determined from Solar radiation observations at the National Observatory of Athens over the period 1955–1972 are analysed. Mean daily turbidity lies between 0.020–0.100. Turbidity is higher in summer than in winter. The main factor determining the turbidity is the air mass type. The scavenging by rainfall probably has a considerable effect in determining this distribution. There is some evidence of a trend of increasing turbidity during the period.

Notes: Abstract Fourier transforms of the theoretical gravity effect due to a two-dimensional asymmetrical triangular prism have been derived. Evaluation of the parameters from the analysis of the Fourier Spectra has been outlined.

Notes: Abstract A seismic refraction investigation across the southern part of the Oslo Rift has been made, based on quarry blasts at three localities. The study shows a three-layered crust with the followingP-wave velocities: $$V_{P_{g(av)} } = 6.20 km/s, V_{P_b } = 6.60 km/s, V_{P^x } = 7.10 km/s$$ . $$V_{P_n } $$ the upper mantleP-wave celocity, is 8.07 km/s. The velocity-depth relationship for the uppermost crust, obtained by solving the Wiechert-Herglotz integral equation numerically, shows a continuously decreasing velocity gradient in the region of the Oslo Rift which approaches zero at a depth of 9 km, the corresponding increase in theP-wave velocity being from 5.55 km/s to 6.34 km/s. The interface separating the subsurface layer ( $$V_{P_b } $$ =6.60 km/s) from the uppermost layer $$(V_{P_{g(av)} } = 6.20 km/s)$$ , interpreted as the Conrad discontinuity, is essentially horizontal in the investigated part of the Oslo Rift at a depth of approximately 15 km. A deep crustal layer with aP-wave velocity of 7.10 km/s appears to be related to the rift, though the top of this layer extends somewhat eastwards beneath the Precambrian rocks from the southern part of the rift at a depth of approximately 20 km. The Moho discontinuity is elevated beneath the Oslo Region compared with the surrounding area. A broad ‘regional’ gravity high of about 45 mgal is observed along the entire rift zone. It is suggested that this anomaly is caused by the elevation of the sub-Conrad and Moho discontinuities during the rifting processes.

Notes: Abstract Seasonal and monthly global patterns of outgoing longwave radiation, albedo, absorbed solar radiation, and net radiation have been derived from scanning radiometer observations aboard the NOAA polar orbiting satellites since June 1974. These patterns, along with patterns of interannual differences in seasonal and monthly heating, are examined for the three summers of 1974–76 over the Eastern Hemisphere in relation to the variations in the summer monsoon and the major circulation features. During portions of the summer of 1975 the monsoon was more active than in 1974 and 1976, as evidenced by increased albedo and decreased longwave radiation over large sections of India, the Indian Ocean, Southeast Asia, and the Western Pacific. The roles of clouds, snow cover, and other surface characteristics in modulating the radiation balance and circulation are discussed. The pre-monsoon radiative heating in spring is examined with respect to monsoon onset and intensity in the three years.

Notes: Abstract Seismic velocity anisotropies measured in underground mines are compared within situ stress measurements in these mines. These underground data are also compared with seismic velocity anisotropies observed by large scale seismic sounding conducted from the earth's surface, The velocity anisotropies are about 10% and the data obtained by different methods on different scales and frequencies agree with each other. The directions of largest and smallest velocities coincide with the largest and smallest horizontal stresses, respectively. These results suggest that the direction and magnitude of stresses in potential mining areas could be estimated from velocity anisotropies observed in seismic prospecting of the area.

Notes: Summary Focal mechanisms of 74 shallow and 16 intermediate earthquakes (1964–1970) in the Kamchatka-Commander region are discussed. Regional stress systems and the nature of faulting are analyzed. Complex stress fields in the Kamchatka-Commander region and variable aftershock processes of strong Kamchatka earthquakes show the existence of heterogeneities of the active seismic zone in the Region.

Notes: Abstract The source parameters, moment, stress drop and source dimension are estimated for 61 events from the January 1975 Brawley earthquake swarm. Earthquakes studied range in local magnitude from 1.0 to 4.7. Stress drops range from 1 to 636 bars and increase with source depth. It is estimated that the sedimentary structure of the Imperial Valley amplifies shear waves by a factor of 2 to 3 in addition to the free surface amplification of 2. Estimates of moment from 10 sec surface waves are 4 to 6 times larger than the moment estimated from the relatively flat part of the local body wave spectrum at 1 sec. This may be due to after-slip on the fault, a long thin fault, or partial stress drop. It is shown that the experimentally determined ratio of stress drop to apparent stress should be approximately 4.0 when spectrum integration is used to obtainS-wave energy and theP-wave energy is 1/3 theS-wave energy.

Notes: Abstract This paper is a review of the theoretical and observational evidence bearing on the magnitude of the shear stress which acts on the base of a lithospheric plate. Estimates based on the viscosity of the upper mantle do not yield useful limits. Arguments based on the thermal stability of the upper mantle indicate that the basal shear stress is no larger than a few bars. An indirect measurement of the rheology and shear stress can be made by studying the diffusion of stress and displacement following a large decoupling earthquake. When applied to the 1965 Rat Island Earthquake, this method yields a basal shear stress of about 2 bars. These results indicate that for small plates the forces produced by basal shear stress are probably small in comparison with forces acting on plate boundaries. To a first approximation, the smaller plates act as if they were decoupled from the mantle below. These stress estimates lead to a model in which the motion of the smaller lithospheric plates is governed almost entirely by the forces acting on their edges. Forces due to basal shear stress may be comparable to forces acting on the edges of large lithospheric plates. Thus, complete decoupling may not be a good approximation for such plates.