The yellow colour of the lens of the grey squirrel (sciurus carolinensis leucotis).

1. The absorption spectrum of the lens of the grey squirrel (Sciurus carolinensis leucotis) has been measured, revealing an absorption maximum at 370 nm. Peak densities in the intact lens ranged from 12 to 20.2. This peak is not present in the lenses of horse, cow, pig, dog, cat, ferret (Mustelo furo), or guinea-pig (Cavia porcellus).3. The pigment responsible for this absorption is water-soluble and aqueous extracts have been examined. Protein-free aqueous extracts show an additional maximum at 265 nm, which can only partially be accounted for by the presence of ascorbic acid.4. The absorption spectrum of extracts of lens material from the ground squirrel (Citellus mexicanus) also had maxima at 265 and 370 nm.5. Chromatography of the protein-free solution separated two yellow components, both of which had a yellow fluorescence. The faster component had a very similar absorption spectrum to the original protein-free solution.6. Possible functions of the yellow pigment are discussed.