310 Mr. B. Swinhoe on Formosan Ornithology. 
head dark grey. In the island of Formosa the Budytes has the 
head uniform in colour with the back, and a yellow eyestreak in 
the adult plumage, being (except perhaps in the rather darker 
ear-coverts) barely distinguishable from the form peculiar to the 
British Islands. Indeed, so similar are the birds from these two 
widely separated localities, that I can scarcely do otherwise than 
regard them merely as varieties of the B. flava , their aber¬ 
rancy from the typical colour and their cosimilarity being due 
to some insular and climatal causes which we cannot just now, 
with any certainty, fathom. The peculiar greenness of the head 
is constant in all my adult specimens, with one or two excep¬ 
tions, which have more or less grey on the forehead, and an in¬ 
clination of the eyebrow and chin to be white instead of yellow. 
This would doubtless likewise be found if a large series of British 
skins were examined. This apparent desire of nature to revert 
to the typical colour, and the absolute identity of the two forms 
in immature and undress plumage, resolve me in setting down 
the Formosan as a variety; for if we are to regard species as 
special creations, how can we reconcile the fact of two islands, 
separated by an entire hemisphere, producing the same form 
almost entirely restricted to themselves, and represented on 
their opposite mains and throughout the intervening vast tract 
of land by a single species, of which specimens procured from 
the extreme east and extreme west are positively identical? 
The Yellow Wagtail is with us, in Formosa, a constant resident, 
assembling in winter in large parties and remaining about the 
fields. In spring it pairs, and scatters itself about the country, 
resorting chiefly to the hill-side streams for the purposes of nidi- 
fication. I suspect also that a good many repair to Japan for 
the summer. 
79. Anthus agilis, Sykes. 
A. arboreus (var.), f Fauna Japonica/ tab. 23. 
This Pipit is abundant in winter in all groves and copses, 
feeding about under the shadow of the trees. The younger birds 
are greener on the back and distinctly spotted: in this plumage 
they might almost be mistaken for the European A. arboreus . 
In the adult the upper parts become more sombre and the spots 
