Preliminary observations show that the pigmentation of eggs and other tissues in conifer sawflies is a valuable taxonomic criterion when the colour can be described objectively in such a way as to allow mathematical analysis of the data. Reproducible semi-integral attenuance spectra covering the spectrsl range 30 kc./cm. to 13 kc./cm. are obtained usins Shibata's opal glass technique for the examination of translucent material. Tfiese spectra are plotted as the log of the semi-integral attenuance and analyzed both qualitatively for positions of maxima and minima, and quantitatively for the relative attenuance level at given spectral positions. The homogeneity of quantitative data from different samples is tested graphically by the triangular co-ordinate method.