timeless-driven, luciferase-reported rhythmicity in cultured antennae. These appendages were taken from transgenic (but otherwise rhythm-normal) flies (cry+, n = 56) or those expressing a cryptochrome mutation (cryb, n = 80) and monitored for luminescence in LD as noted in Figure 1d. Top row, analysis of cry+ specimens; bottom, cryb. The column of panels on the left shows mean luminescence values (across specimens) plotted vs. time. Mean numbers of counts/hour/specimen-pair (for antennae of each genotype) are given in the upper right hand corners of this column. The gray shadings surrounding the plotted lines denote standard errors of the mean (SEM). The second column from the left shows detrended, normalized data. The fluctuating luminescence values re-plotted in this way reveal a genotype difference: the cry+ antennae were (on average) smoothly rhythmic (given the fairly clean, sinusoidal oscillations of tim-controlled luciferase activity), whereas the cryb group gave bumpier results. However the detrending treatment of both data sets reveals both groups of antennae to be periodic for this enzymatic reporting of clock-gene expression. The third column from the left shows the results of applying an autocorrelation function to the luminescence data, which evaluated the detrended, normalized data from each group. The shapes of and values associated with these correlograms indicate that each data set is rhythmic (confirming the impression from the second panel). The asterisk above the third peak (offset from 0, for which the data were perforce perfectly correlated with each other) indicates the point used to assess the Rhythms Index (Rl), a measure of rhythm strength (see text). The right-most column shows the results of maximum entropy spectral analyses (MESA), a method applied independently to estimate periodicity in these time series. The abscissa positions and heights of the peak in the MESA plots indicate the principal periodicities by which the cry+ and cryb antennae exhibited systematically fluctuating luciferase activity.