Glycol methacrylate is the principle component in the JB-4 embedding medium. We used glycol methacrylate monomer as a liquid clearing and mounting medium. However, glycol methacrylate has a low viscosity, and this makes it difficult to mount and orient the specimen for photographing. To get around the problem, we mix the more viscous polyethylene glycol (PEG) methacrylate (PEGM) with glycol methacrylate to adjust its viscosity. The ratio of the mixture can be determined empirically, given that viscosity of PEGM may differ between batches. For PEGM with shorter side chain (e.g. Sigma 409537), it is okay to use 100% PEGM. To clear the embryos, embryos are first dehydrated through a ethanol series (50%, 70%, 80%, 90%, 95%, 100%, 100%) and then incubated in glycol methacrylate (e.g. 2-hydroxyethyl methacrylate (HEMA) monomer; Electron Microscopy Sciences Cat. No. 16800) for at least an hour. Then, incubate the specimen in polyethylene glycol methacrylate overnight. Mount the specimen in polyethylene glycol methacrylate for observation and imaging.