The Intra-Ocular Colour-Filters of Vertebrates

OPHTHALMOLOGY appear to be the first confirmation of those of Leydig, made in 1853 (see Schultze).Lacerta ocellata, Gerrhonotus scincicauda and Crotaphytus collaris, each representative of a family of bright-light lizards, showed colourless and deep lemon droplets in co. 1:4 ratio.A fossorial lizard (Aniella pulchra) on the other hand revealed only unpigmented droplets which, unlike those of Xantusia, had an extremely pale yellow-green fluorescence.A number of diurnal wild birds37 were studied and found to have richly pigmented droplets.Strix v. varia, however, had only a few yellow droplets, the rest being unpigmented but faint bluishgreen-the same situation as reported for S. aluco by Erhard (1924).The same reduction of red droplets noted by Erhard in a woodpecker was seen in the three American woodpeckers examined: Dryobates pubescens medianus, Melanerpes erythro- cephalus and Colaptes auratus luteus averaged only 10.4 per cent.red droplets, as compared with 11 per cent.for the European wood- pecker and 20 per cent.for passerines in general.It was found almost impossible to locate the foveae in the fresh retinae of shot birds, as the post-mortem drainage of the aqueous produced extensive retinal detachment.The foveae were observed, however, in three species secured alive and tightly garrotted to maintain the intra-ocular tension during enucleation.In all of these-Falco s. sparverius, Passer domesticus and Dryo- bates pubescens medianus -the foveae contained only yellow droplets.Thefoveaof Dryoba'teswas found to be relativelyshallow, which is in keeping with the visual habits of this type of bird.Only in Colaptes auratus luteus were any pigmented droplets found which were strongly greenish-yellow.In no bird was any- thing comparable to the "pure grass-green" droplet (reported for Milvus regalis by Kiihne) found.All oil-droplet pigments appear to be certainly carotinoids; they are easily soluble in alcohol, etc., and are present in normal amounts in albinotic birds (see Krause, 1894).The greenish-yellow, yellow-orange, and red-purple pigments extracted from whole retinae by Kiuhne were named by him Chlorophan, Xantophan, and Rhodophan respectively.Kiihne realized that two or all of these pigments might be present in a given droplet in particular proporti6ns.Waelchli (1883), repeating the pioneer microspectroscopic work of Talma (1873), found the transmission spectra of the droplets themselves to differ from those of Kiihne's extracts.Assuming each droplet to contain but a single pigment, Waelchli renamed the pigments Sphaero-37 Falco s. sparverius,