摘要:

Summary1. The concept of a topographical representation of sensory surfaces on the mammalian cerebral cortex is now well established. Furthermore, there is claimed an expanded representation for those sensory surfaces associated with behavioural specializations.2. In the case of the visual system, the field of view associated with the retina is projected on to the striate cortex, with the central fovea or point of most acute vision occupying a disproportionately large area of representation.3. The term ‘cortical magnification factor’, denoted by M, has been introduced to indicate, for a given eccentricity and meridian, the linear distance in mm along the primary visual cortex concerned with each degree of visual field.4. The quantitative accuracy of this function subsequently has been improved and a relationship established between cortical magnification and visual acuity in man.5. On the basis of spatio‐temporal investigations across the visual field under levels of photopic adaptation, visual scientists have utilized retino‐cortical magnification to reconcile aspects of structure and function in the human visual

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1986.tb00463.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Summary1. Renewed interest in the role of changes to developmental regulation in organisms has highlighted the importance of heterochrony in the evolution of the Metazoa.2. Beecher's interpretation of the evolution of the Trilobita as having been principally by peramorphosis is examined, as is the view of later workers, principally Stubblefield and Hupé, that paedomorphosis was a dominant factor in trilobite evolution.3. Both peramorphosis and paedomorphosis are considered to have been important in trilobite evolution.4. The role of paedomorphosis in the evolution of major morphological novelties is critically examined. Its importance in changes to the structure of the glabella is discussed and new terms proposed to describe the ontogenetic and phylogenetic state of the glabella.5. The highly variable nature of early Cambrian trilobites, in particular the large degree of ontogenetic change, is considered, along with possible poor developmental control of the growth and moulting hormonal systems, to have been significant in providing a high degree of intrapopulational morphological variability. Selection of these heterochronic variants was responsible for the rapid diversification of the Trilobita during the Cambrian

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1986.tb00464.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SummaryThe objective of this review was to develop a broader, more biological, overview of puberty, as opposed to the more limited, laboratory‐dominated, view that has emanated from experimental physiology. Three conceptual schemes form the basis for our broader perspective. The first deals with the ways in which genes and environmental factors interact to program the timing of reproductive development. The second focuses on the ways environmental factors interact with each other to influence puberty. The third relates the genetic and environmental controls to specific endocrine and neuroendocrine pathways of action.The more traditional approach of studying domesticated animals under carefully controlled conditionspredeterminesone's conclusions. One logically will conclude that the final stages of reproductive development are rather rigidly determined genetically and not greatly subject to environmental regulation, except for obviously adaptive pheromonal and photoperiodic regulation. One also will search within the reproductive axis itself for the final developmental step that allows functional fertility. In contrast, a more biological view suggests that for most mammals puberty is a highly labile process subject to several kinds of environmental influences that operate at many times during a mammal's life. Furthermore this perspective suggests that the final developmental step allowing fertility onset normally will occur outside rather than within the reproductive axis proper. This conclusion has a potentially great impact upon the way we look at the organization of the brain and endocrine system and in the way we choose animal models for studying human puberty and the types of controls we stud

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1986.tb00465.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1986.tb00466.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY