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Despite the fact that certain prominent structures such as theeight comb-rows at first suggest an octomerous radial symmetryin ctenophores, close examination of their anatomy reveals ratherthe existence of two main planes, the sagittal and the transverse.Further, in certain forms in which one plane or the other hasbecome predominant, an apparent bilateral symmetry emerges. Relationships between anatomical and physiological symmetrywere looked for by studying the behavior of Beroe ovata andBeroe forskalii, both with regard to coordinated ciliary movementsbetween the comb-rows, and to the postures assumed during locomotion,balance, and rest in intact animals, and in animals from whichthe aboral organ had been removed. Swimming behavior is found to exhibit an octomerous functionalsymmetry. Bendings and vertical balance, however, show a tetramerousorganization. In the last case the unique properties of thestatocyst, with a structure characteristic of a regulator ofcybernetic patterns, the machines of which are the comb-rows,permit the most efficient integration of all the phenomena involvedin maintaining the vertical position. Finally the resting horizontalposition reflects a physiological bilateral symmetry basic tothe sagittal plane.  相似文献   

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Christopher J.  Feare Jeremy  High 《Ibis》1977,119(3):323-338
The aim of this paper was to assess the status of migrant shorebirds in the Seychelles. Most observations were concentrated on two areas: a 6 ha mudflat at Victoria, Mahé, and open areas of Bird Island. A systematic list of all shorebirds that have been recorded in the Seychelles is given, including data on abundance and their incidence on other islands of the Malagasy region. Most of the Seychelles migrants probably originate from the north and east, i.e., the central and eastern Palaearctic, and arrive after a sea-crossing of over 1600 km. Highest numbers of species and of individuals occurred in the Seychelles during the northern winter, but about one third of the species recorded were also present, in reduced numbers, in the summer. Few birds in breeding plumage were seen; probably most birds, especially those which summered, were immature. Numbers of both summering and wintering birds varied from year to year, these variations probably being related to breeding success at higher latitudes.  相似文献   

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Abstract:  The meaning of modifications in septal spacing that often coincide with maturity in extant Nautilus and fossil nautiloids, and also in ammonoids, remains controversial. In the Callovian nautilid species Paracenoceras marocense Miller and Collinson, 1952 , the extent of decrease in septal spacing and the exceptional number of approximated septa are correlated with an unusual positive ontogenetic allometry in whorl-width expansion. This allometric growth implies that the threshold weight of the animal, requiring the formation of a new chamber to maintain near-neutral buoyancy, was reached for an increasingly shorter angular length of shell added to the aperture. Thus, the available space for the newly forming chamber behind the advancing body was reduced accordingly. Ontogenetic modifications in septal spacing are linked to relative growth of the animal. The flexibility in the mechanisms of buoyancy regulation would be expected to have been a critical factor affecting the possible set of ontogenetic trajectories in chambered cephalopods and thus the realm of variation upon which selection could act.  相似文献   

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In this paper we argue that the consensus around normative standards for the ethics of research in clinical trials, strongly influenced by the Declaration of Helsinki, is perceived from various quarters as too conservative and potentially restrictive of research that is seen as urgent and necessary. We examine this problem from the perspective of various challengers who argue for alternative approaches to what ought or ought not to be permitted. Key themes within this analysis will examine these claims and argue they have implications for the interests of the research subject, research governance and regulation. Using our work with TREAT‐NMD, the neuromuscular clinical trials network, we posit that there is a place for advancing the discourse of moral rights and moral duties in the context of research, especially from the perspective of patients and their families, and for including the politics of patient activism and empowerment. At the same time we remain vigilant to the danger that the therapeutic misconception and other serious vulnerabilities for the patient population in clinical trials, are at risk of being overlooked.  相似文献   

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Sensory analysis has traditionally played a prominent role in quality control for food products. More and more principles from sensory analysis are also applied in the area of food product development, bringing sensory analysis more closely into the domain of marketing. Unfortunately, in practice integration between sensory and marketing practices is far from optimal. Differences in basic orientations between sensory and marketing are a major source contributing to this defective cooperation.
Sensory analysis has traditionally been product oriented with an emphasis on internal validity of the test results. Implicitly or explicitly this approach emphasizes the relationships between sensory evaluation and characteristics of the product. Marketing, on the other hand, stresses the external validity of test results: the extent to which test results can be generalized to market behavior. Emphasis on external validity requires an approach to sensory analysis that is fundamentally different from current sensory practice in terms of type of respondents, type of stimuli, scaling procedures adopted and test circumstances.
Closer integration between the product and consumer oriented approach to sensory analysis may contribute to the success of product development in the food industry. The literature suggests several factors that may contribute to a more fruitful cooperation between the two approaches to sensory analysis. The company's senior management plays a central role in the achievement of this integration by providing an infrastructure (in terms of personnel, organizational structure and financial resources) that paves the way for closer cooperation.  相似文献   

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Shells of Calliostoma zizyphinum taken from Strangford Lough,N. Ireland are divisible into three distinct colour forms: white(=var lyonsi) intermediate (a pale variegated form) and purple(a dark variegated form). The predominance of white and paleshelled individuals within and the absence of white Calliostomaoutside the lough was confirmed. The proportions of animalswith white and variegated shells at selected sites were almostidentical with those previously documented, suggesting a temporalstability of colour form ratios. No differences in shell thicknessand pedal adhesion were demonstrated between these forms. Snails with white shells reflect radiant heat better, have lightercoloured feet, move more rapidly, show a greater incidence ofshell repair and are more frequently exposed on weed at lowtide, than those with either intermediate or purple shells.Increased proportions of white individuals may be associatedwith high population densities. Under such circumstances, itis suggested that increased mobility may, by increasing dispersion,reduce intraspecific competition. In the event of exposure atlow tide a white shell would help minimize thermal stress. (Received 9 February 1987;  相似文献   

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Introduction:  An increased risk of cervical dysplasia has previously been reported in lupus. The role of traditional related risk factors are unclear. Persistent infection with certain genotypes of Human Papilloma Virus termed high risk (HR-HPV) is considered a prerequisite for the development of cervical cancer.
Methods:  A total of 141 SLE patients fulfilling the ACR criteria for lupus were enrolled into the study. They were compared to 138 control patients who were due to attend for a routine cervical smear. Each patient completed a cervical cancer risk factor questionnaire. A cervical smear was taken and residual material used to test for the presence of HR-HPV using a hybridisation microplate assay. Positive samples were then genotyped.
Results:   
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Abstract:  A large number of fenestrate bryozoan species were named in 'A Synopsis of the Characters of the Carboniferous Limestone Fossils of Ireland' by Frederick M'Coy (1844). At the same time, M'Coy named the bryozoan genera Ichthyorachis , Ptylopora and Polypora , each of which by monotypy or by subsequent designation was based on new species within that work. Subsequently, d' Orbigny (1849) named Fenestrellina with the type species Fenestella crassa M'Coy, 1844 as type species; Miller (1961) named Parafenestella with the type species Fenestella formosa M'Coy, 1844 as type species; and Wyse Jackson (1988) named Baculopora with the type species Vincularia megastoma M'Coy, 1844. We re-describe here in more detail than previously the fenestrate type species originally published in M'Coy (1844), provide diagnoses of the genera, and compare the nineteenth century genera with more recently named genera that have been discriminated specifically from them.  相似文献   

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