180
THE ESSEX NATURALIST.
1. That complete albinism may be developed.
2. That complete albinos ever revert, even partially, to
normality.
3. That the cases of partial albinism, which have persisted or
increased, were congenital or developed.
The other phases of heterochrosis are much less understood.
Beyond the fact that both can be produced artificially we know
practically nothing about xanthism and erythrism. Melanism
can be produced by feeding, and the pattern of the feather is
retained by affected birds.
REFERENCES.
1845. On the Transmission of Colour by the White or Pied Pheasants
to their Young. "W.H.S." Zool., pp. 873-6.
1852. Instance of a Blackbird turning white from Fright. Rev. A. C.
Smith. Zool. pp. 3576 and 3665 ; J. Johnson, p. 3632.
1853. Observations on the General Colour and the Occasional Variations
in the plumage of Birds. Rev. A. C. Smith. Zool., pp. 3969-80.
1896. A Dictionary of Birds. A. Newton. 8vo. London.
1910. A History of Birds. W. P. Pycraft. 8vo. London.
1911. A Monograph of Albinism in Man. Karl Pearson, E, Nettleship
and C. H. Usher. Drapers' Company Research Memoirs.
Biometric Series, Nos. 6, 8, and 9.
1916. A Study of the Structure of Feathers with reference to their taxo-
nomic significance. Asa C. Chandler. University of California
Publications in Zoology, Vol. 13, No. 11, pp. 243-446, pls. 13-37,
seven text figures.
1923. The Biology of Birds. Prof. J. A. Thomson. 8vo. London.
Part 3.—Abnormal Colouration in Essex Birds.
The purpose of this part of the paper is to collate all known
and recorded instances of heterochrosis which have occurred
in the county, to arrange them systematically, to make deduc-
tions therefrom, and to consider these results in relation to the
subject as a whole. This is probably pioneer work, and it is
hoped that it will be of some missionary service, and place the
subject, so far as the county is concerned, on a foundation which
will facilitate and simplify the work of others who may choose
to pursue the problems of the question. The systematic list
which follows has claims to being of a complete nature. It
covers all the ground which was explored for "A History of the
Birds of Essex," with the addition of a search to date of "British
Birds" (Mag.), "The Essex Naturalist" and "The Field."