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R. Ruggles Gates . 
CHAPTER XII. 
Grthogenetic Characters. 
In previous chapters we have drawn a contrast between (a) 
karyogenetic characters originating as mutations in the germplasm 
and affecting every nucleus, and (b) organismal characters which 
belong to the organism as a whole, show recapitulation, and 
probably originate as environmentally impressed modifications of 
the cytoplasm. In this chapter we wish to consider briefly 
orthogenetic characters, which appear to stand midway between 
these two categories. Like the former they are germinal in origin, 
and like the latter they show recapitulation. But they differ from 
the recapitulatory characters previously considered, in that their 
origin is apparently not adaptational but on the contrary 
independent of environment. We will refer only to three cases 
from the recent experimental work with animals. 
It is a well-known fact that in many birds the juvenile plumage 
differs from that of the adult, and usually at least represents a less 
specialized and presumably ancestral type of plumage. One of 
the most striking cases, recently studied by Beebe (1914), is in the 
white ibis, Guava alba. In the young chick the head and neck are 
covered with black down, becoming smoky gray over the greater 
part of the body except the under parts, which are white. In the 
juvenile and post-juvenile stages this is gradually replaced by white 
feathers, until late in the second year the birds are pure white with 
scarlet legs and bill. It seems clear that such a white bird has not 
originated through a mutation, and that the ontogeny represents a 
gradual transition from a dark-coloured ancestor. It is an 
interesting fact that the white loral spots in the young chick, 
which quickly disappear, apparently represent the permanent facial 
marking of a related ibis, Plegadis autumnalis. This would appear 
to be one of the few cases in which a specific (generic) difference is 
at the same time a recapitulatory character. 
Whitman’s (1919) recent posthumous volumes on orthogenetic 
evolution in pigeons cite a number of cases of juvenile plumage as 
recapitulatory stages furnishing evidence of orthogenetic develop¬ 
ment. Whitman’s study of the wing patterns of pigeons is perhaps 
the most prolonged and intimate investigation which has ever been 
made of a single character. Reading the series in the opposite 
direction from Darwin, he concluded that the primitive condition 
was a uniform chequered pattern covering the whole wing, as in 
