This article aims to examine the di¨erences in the behaviour of productivity across the European regions. First, we give an overview of regional convergence of productivity in the European Union. Signi®cant regional di¨erences emerge from the detailed analysis of the evolution of productivity that follows. We note that those di¨erences can even be observed in relatively homogeneous regions (peripheral, central, old industrialised, etc.).A new methodological approach is introduced with the aim of exploring in greater depth this diversity, especially in the evolution of labour productivity. A total of 97 regions from the European Union have been selected in order to verify some speci®c di¨erences in productivity, employment and GVA growth rates. Despite the global trend towards convergence in productivity, this article reveals that signi®cant regional di¨erences persist. Finally, a regional typology is presented.

The differentiation of tissues and organs requires that cells exchange information in space and time. Spatial information is often conveyed by morphogens: molecules that disperse across receiving cells to generate signalling gradients. Cells translate such concentration gradients into space-dependent patterns of gene expression and cellular behaviour. But could morphogen gradients also convey developmental time? Here, by investigating the developmental role of Hh on a component of the Drosophila visual system, the ocellar retina, we have discovered that ocellar cells use the non-linear gradient of Hh as a temporal cue, collectively performing the biological equivalent of a mathematical logarithmic transformation. In this way, a morphogen diffusing from a non-moving source is decoded as a wave of differentiating photoreceptors that travels at constant speed throughout the retinal epithelium.

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