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\section{Introduction}   In recent years the focus of much star formation research has been on the relationship between the immediate star formation environment and the evolution of protostars. The data from the last generation of orbiting observatories has invigorated work toward understanding the formation of filamentary structures in molecular clouds, and the condensation of dense star forming cores form these filaments. [BLAH BLAH ETC REDO THIS PARAGRAPH]  Observations with the Herschel satellite have revealed that the backbone of molecular clouds is a compex network of connecting and interacting filaments \citep[e.g.][]{2010A&A...518L.102A,2010A&A...518L.100M,2011A&A...529L...6A,2012A&A...540L..11S} \citep[e.g.][]{2010A&A...518L.102A,2010A&A...518L.100M,2011A&A...529L...6A,2012A&A...540L..11S}. The dynamics of this web of dense molecular gas not only determines the evolution and stability of molecular clouds, it also regulates their condensation into stars. Molecular cloud cores and single low-mass stars are almost always found in filaments, often aligned like pearls on a string \citep{http://adsabs.harvard.edu/abs/2002ApJ...578..914H,http://adsabs.harvard.edu/abs/2008ApJ...672..410L,2010A&A...518L.102A}.  Recently \citet{2013A&A...554A..55H} presented observations of a prominent filamentary feature in Taurus, dominated by the L1495 cloud \citep{1962ApJS....7....1L} and the several dark patches \citep{1927cdos.book.....B}. Hacar et al. observed the region in the moderate density tracer C$^{18}$O, obtaining spectra along a $\sim 3$ pc length of the region. Analysing the filament in the resultant position--position--velocity space, they found the intriguing result that the gas along the ridge is organized in velocity-coherent filamentary structures, with typical lengths $\sim0.5$ pc. Each filament is internally subsonic or transsonic, though the collection of filaments is characterised by a mildly supersonic interfilamentary dispersion of $\sim 0.5$ km s$^{-1}$.  Multiple velocity components along a single line of sight have also been observed in Serpens South \citep{2013ApJ...778...34T}; this feature may be common one in young star forming sites.