1. The free lutein and astacene in the muscles may contribute about half the carotenoid found in the ova of spawning female trout. The esterified forms of these pigments in the chromatophores of the skin are not, however, depleted.
2. Lutein and astacene are transferred without apparent loss from the yolk of the egg to the body of the embryo, principally during the later part of the larval period. The rate of pigment transfer appears to be related to the growth rate of the posterior end of the embryo, and corresponds cioseiy with the visible development of xanthophores and erythrophores.
3. Removal by operation of about 90% of the yolk carotenoids results in larvae which are slightly smaller than normal and with very few pale chromatophores, but with no other apparent defect.
4. Lutein and astacene in the yolk are the free hydroxy-carotenoids, but are esterified in the embryo. About two-thirds of the pigment of the embryo was found to be in the skin and fins at metamorphosis.
5. β-Carotene, which is present in freshly spawned ova, was not detected in the embryo at any stage of development.