Mr. H. Seebohm on the Genus Himantopus. 227 
to believe that the former became Stilts and the latter 
Avocets; but inasmuch as interbreeding could take place 
between the birds of each bay and those of the next, along 
the whole line in one direction, it can scarcely be doubted 
that at first the Stilts were connected by a series of inter¬ 
mediate forms with the Avocets. The next cause of isolation 
(which was probably complete) was most likely a glacier 
stretching across the north pole from the Rocky Mountains, 
either to Novaya Zemlya or to the mountains of Eastern 
Siberia. This must soon have been followed by the evacua¬ 
tion of the Polar basin, and the emigration of the birds in 
four parties along the four shores leading to the south. 
The causes already explained must have produced an emi¬ 
gration of Stilts along one coast of the Atlantic, an emigra¬ 
tion of Avocets along the other, whilst the emigration along 
the two coasts of the Pacific must have consisted on the one 
side of Avocets with a strong strain of Stilt in them, and on 
the other of Stilts with a strong strain of Avocet blood. 
The next step to take is to examine the ten species of the 
genus, and ascertain if all four parties of emigrants have left 
descendants, and to determine by what characters they may 
now be detected. The four groups of which we are in 
search are Stilts, Semi-stilts, Avocets, and Semi-avocets. 
The three first species on the list, H. avocetta , H. rubricollis, 
and H. americanus , are unquestionably thorough-bred Avo¬ 
cets, diagnosed as mantle white, scapulars and secondaries 
for the most part white. The five last species on the list, 
H. mexicanus , H. hrasiliensis, H. leucocephalus, H. novae - 
zelandice, and H.melanopterus, are as unquestionably thorough¬ 
bred Stilts, having all the parts mentioned above black in¬ 
stead of white. These are the important characters which 
date farthest back, but it is worthy of note that in these two 
groups the black mantle, &c., is correlated with a straight 
bill, very slightly webbed feet, and the absence of a hind toe; 
whilst the white mantle is correlated with a recurved bill, 
strongly webbed feet, and the presence of a hind toe. We 
have now two species left, H. andinus and H. pectoralis. The 
former is called an Avocet, and the latter a Stilt, by the 
