Our finding that perineurial and subperineurial glia express PER protein is consistent with a recent study of the surface glia transcriptome of adult Drosophila compared to the transcriptomes of all neurons, all glia, and to total brain lysates (DeSalvo et al., 2014). While not the focus of the study, their data do list per mRNA and other circadian clock genes as expressed in the surface glia (DeSalvo et al., 2014). Moreover, the core clock gene Clk was identified as one of the top 50 genes enriched in surface glia when compared to all glia (DeSalvo et al., 2014). The perineurial and subperineurial glia have distinct non-overlapping roles in the formation and maintenance of the blood-brain barrier that are not well understood (Awasaki et al., 2008; DeSalvo et al., 2014); the presence of the circadian clock in these cells may help to understand their functioning in the future.