In partially molten regions of the Earth, crystalline grains and magma coexist to form a two-phase rock. The solid grains within the rock provide a viscously deformable framework with magma residing in an interconnected network between grains. To preserve the observed chemical disequilibrium between the erupted magma and the mantle rock through which it travels, melt must segregate into and flow through high-permeability channels to reach Earth's surface from its origin at depths approaching 100 km. Deviatoric stress profoundly influences melt distribution in a viscously deforming partially molten rock, establishing a coupling between deformation and melt distribution. As a partially molten rock deforms, this coupling leads to a grain-scale alignment of melt and a rock-scale organization of melt into melt-enriched ' and, thus, highly permeable ' shear zones. My talk focuses on experimental investigations of the role of stress on spontaneous melt segregation within deforming partially molten rocks in the context of recent theoretical developments of constitutive laws for viscosity and field observations of anastomosing channel networks.