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SummaryPhylogenetically mammalian platelets are an apocrine secretion from nucleated thrombocytes, and biologically the number of circulating fragments is irrelevant compared with their total mass and biochemical function. The literature on human genetic derangements affecting the circulating platelet mass is reviewed. The product of platelet count and platelet volume is shown to be “canalised” since many congenital forms of thrombocytopenia are associated with a reciprocal increase in the mean platelet volume. Considerations of platelet size are essential since macrothrombocytopenia is a racial characteristic of many Mediterranean peoples and probably also occurs frequently in others races. The location of platelet disorders in relation to the phylogenetic canal provides an objective classification which has diagnostic, therapeutic and prognostic significance.

Synopsis A theory is presented for piping mechanism in cohesive soils which is also applicable to cohesionless soils. Taken into consideration are the various forces acting on a soil element, namely the drag force due to water flow, the submerged weight and the soil tensile strength. The theory explains the high resistance of cohesive soils to piping. It was found that the safety factor against piping in a cohesive soil is inversely proportional to the size of the aggregate that may be washed out. An assessment of the size of aggregate is made possible by the theory developed. Experimental results are presented and correlated with the theory. Cet article présente une théorie sur le mécanisme de canalisation pour les sols cohérents. Il est tenu compte des forces diverses agissant sur un élément de sol, à savoir la force de résistance dûe à l'écoulement de l'eau, le poids submergé et la résistance à la traction du sol. La théorie explique la grande résistance des sols cohérents au transport par canalisation. On a trouvé que le facteur de sécurité centre les canalisations pour un sol cohérent est inversement proportionnel à la dimension de l'agrégat pouvant être transporté La théorie développée rend possible l'evaluation de la dimension de l'agrégat. Les résultats expérimentaux sont exposés et mis en corrélation avec la théorie.

Starting from a genetically variable stock homo- or hemi-zygous for Bar two selection lines were set up, one selected for decreased sensitivity to the effect of larval temperature on eye size (‘canalization line’), the other for increased sensitivity (‘anti-canalization line’). In each generation a sample of larvae was grown at 25°C. throughout life and another sample at 25°C. for the first 48 hours, followed by 18°C. until emergence. In the canalization lines a selection was made of individuals (five males and five females out of 100) least affected by the temperature treatment and the anti-canalization line for a similar number most affected by the treatment. These ten males and females were allowed to mate at random and from the eggs produced random samples were then treated in the next generation in a similar manner in the two temperatures. Precise counts of facet numbers on the right eyes were made at generations 4 and 9 and it was clear that selection had been effective both in decreasing and increasing temperature sensitivity.The whole canalization line can be regarded as a population which has been subjected to disruptive selection for two different criteria: one (small eyes) being regarded as adaptive to the low-temperature regine or habitat; the other (large eyes) being regarded as adaptive to the high-temperature habitat. A similar type of analysis can be applied to the anti-canalization line in which, however, the selective values of the phenotype are regarded as reversed in value in the two habitats. The experimental procedure employed involved not only random mating between individuals selected according to these two criteria but also random allocation of the offspring of this panmictic population to the two habitats of the next generation. This corresponds to a natural population in which there is disruptive selection exerted by two different habitats but no habitat preferences exhibited by members of the population. Under these circumstances, in our experiments, disruptive selection produced only rather slight increases in phenotypic variance, which were rather larger in the anti-canalization than in the canalization lines. Possible reasons for the difference between this result and those reported by Thoday and Gibson are discussed, and it is suggested that an important reason may be the slowness of the response to selection in the first few generations in our lines.

On a etudie la canalisation des fragments de fission dans les metaux, en particulier dans le platine et le tungstene. On montre que cette canalisation est tres importante, et que les conditions de canalisation pour les fragments de fission sont plus strictes que pour les particules plus legeres, comme les particules α. La bonne definition des images obtenues par “canaligraphie” permet de penser que cette technique sera tres utile pour I'etude des defauts cristallins dans les metaux. THE CHANNELING OF FISSION FRAGMENTS The channeling of fission fragments in metals is studied, in particular in platinum and tungsten. It is shown that this channeling is very important, and that the conditions of channeling for fission fragments are more rigorous than for lighter particles, such as α particles. The good resolution of images obtained by “channelography” suggests that this technique will be very useful in the study of crystalline defects in metals.

Selection was applied to anterior and posterior scutellar bristles separately and jointly in two populations, one of which straddled the 3/4 bristle threshold and the other the 4/5 bristle threshold. The object was to define the thresholds of the normally canalised 4 bristle phenotype in terms of the component anterior and posterior bristles. Changes in total bristle number (anteriors plus posteriors) at the 3/4 threshold is a function of addition or loss of bristles at the posterior site, whereas changes at the 4/5 threshold exclusively involve anterior bristles. It is concluded that the component anterior and posterior bristles are essentially independent.

IT has been shown by Fermi and his collaborators1 that the efficiency of radioactivation of certain elements by neutron bombardment is greatly increased by surrounding them with water, paraffin or similar hydrogen-containing substances. This effect is attributed to multiple collisions between neutrons and protons, similar to those due to the thermal agitation of gas molecules, producing reduction in speed of the neutrons, which facilitates capture by other nuclei.

Canalisation and threshold effect of the extra scutellar phenotype in Drosophila melanogaster