The distribution of the equivalent width of the different emission lines in the HRS sample. The black line indicates the whole sample of late-type galaxies, the blue line that of galaxies with a normal HI gas content (HI − def ≤ 0.4) and the red one that of HI-deficient Virgo cluster objects (HI − def > 0.4). Each panel gives the total number of available data, the mean value of the equivalent width for the whole distribution (black) and separately for galaxies with a normal HI gas content (HI − def ≤ 0.4; blue) and for HI-deficient objects (red), and the probability that the HI-normal and HI-deficient galaxy distributions are driven by the same parent distribution, as derived by the Kolmogorov-Smirnov (KS) test.