on development of pattern in birds.



183



My suggestion that the development of shaft-streaks accounts

for diversified pattern is not based upon unsupported evidence, since

I noted it in observations on the change of colour in Pyromelana

franciscana (see ‘ Ibis,’ 1897, p. 361), carefully keeping watch on

particular groups of feathers day by day. I also saw the same form

of expansion in the colouring slowly developed in the assumption

of the adult colouring by Paroaria capitata, an account of which

was published in the ‘ Proc. Zool. Soc.’ for 1904, pp. 350-351. I

believe that I have also recorded elsewhere similar facts respecting

the spring growth of colour in the throat-patch of the Grey Wagtail

which I kept caged at the time.


When a dark shaft-streak is divided by a light feather-shaft

it may give rise to the twin-spots which occur in some bird-

plumages, as in Polyplectron (see Darwin’s 1 Descent of Man,’

second edition, p. 659). Still, on all these points we want more

evidence, and that can best be obtained by interbreeding and close

observation.


I have mentioned the Zebra-finch x Bicheno hybrid as indi¬

cating the development of a transversely banded breast from the

crescentic outer borders of the feathers in a common ancestor ; and

in my article on hybrid Ploceidce (‘ Avic. Mag.,’ new series, vol. iv.,

pp. 345-354) I have pointed out the interesting facts which may

be discovered by crossing two species not nearly related. Recently,

while again reading Darwin’s ‘ Descent of Man,’ I came across a

passage which favours the same view. He says : “ The constitu¬

tional disturbance in the offspring, caused by a cross between two

distinct species or races, often leads to the reappearance of long-lost

characters.” Well, among other things I concluded that, as neither

the Zebra-finch nor the Diamond-finch had the remarkable crimson

breast shown by the hybrid depicted on my plate, the ancestor of

these birds must have had crimson on the breast, which had even

been retained in the Painted-finch ( Emblema picta), a relative of the

Diamond-finch ; and I was agreeably surprised later by the discovery,

in an example of the latter which died in one of my aviaries, of

rose-red fringes to several of the breast-feathers, indicating a partial

reversion to this ancestral colouring.


This brings me to the practical object of the present article:



