| Abstrakt: |
. The Pittidae of the subgenus Cervinipitta are practically uniform in the colour pattern of their plumage, but the African forms differ from the remaining (namely, Asian and Australasian) forms of the subgenus in the structure and pigmentation of their green (Tyndall-coloured) feathers. In these feathers, the Africans appear to show certain ancestral characters: small numbers of medullary cells, some of which may contain small, fluctuating amounts of dark-pigmented granules. These characters coexist there with specialized features, which may intensify the colour effect: absence of the granules from most medullary cells and aggregation of such granules in lateral portions of the cortex. In the Eastern forms of the subgenus, the number of medullary cells appears to be secondarily increased, and the amount of granules enlarged and concentrated in axial cells of the medulla-again serving the intensification of the colour. In this way the African and the Eastern branches of the subgenus have undergone divergent specialization in histological details, but show practically identical colour effects. However, the African branch appears to have retained some primitive characters and shows incompletely stabilized conditions. [ABSTRACT FROM AUTHOR] |
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