Wolffian ducts collected from hoxb7 GFP transgenic mice at embryonic day (E)14.5, E16.5, E18.5, and postnatal (P) day 1 (P1). GFP is expressed in the epithelial cells of the ducts, allowing the process of duct coiling to be appreciated. Coiling proceeds from proximal to distal, and is initially two-dimensional at E16.5, and three-dimensional by E18.5. Republished with permission of John Wiley and Sons, Inc., from Hinton et al [174]; permission conveyed through Copyright Clearance Center, Inc.