788 SYSTEMATIC SYNOPSIS.— PYGOPODES. 
as by the feet. Few other birds, such as cormorants and anhingas, resemble the Pygopodes 
in this respect. The legs are so completely posterior, that in standing the horizontal position 
of the axis of the body is impossible; the birds rest upright or nearly so, the whole tarsus 
being often applied to the ground, while the tail affords additional support; progression 
on land is awkward and constrained, only accomplished, in most cases, with a shuffling 
motion, when the belly partly trails on the ground. One species of auk could not fly at all, 
because the wings, although perfectly formed, were too small to support the body. The rest 
of the order fly swiftly and vigorously, with continuous wing-beats. The rostrum varies 
in shape with the genera; but it is never extensively membranous, nor lamellate, nor 
furnished with a pouch. The nostrils vary, but are neither tubular nor abortive. The 
wings are short, never reaching when folded to the end of the tail. The tail is short, never 
of peculiar shape, generally of many feathers; there are, however, no perfect rectrices in 
the grebes. The crura are almost completely buried, and feathered nearly or quite to the 
heel. The tarsus is usually compressed, sometimes, as in the loons, extremely so. The front 
toes are completely palmate in the loons and auks; lobate, with basal webbing, in the grebes; 
the hallux is present and well formed, with a membranous expansion, in loons and grebes, 
wanting in the auks. The plumage is thick and completely waterproof: once observing 
some loons under peculiarly favorable circumstances in the limpid water of the Pacific, I saw 
that bubbles of air clung to the plumage whilst the birds were under water, giving them a 
beautiful spangled appearance. The pterylosis shows both contour and down-feathers, both 
after-shafted; there are definite apteria; the auks have free outer branches of the inferior 
tract-bands, wanting in the loons and grebes. The oil-gland is large with several orifices. 
Among osteological characters should be particularly mentioned the long apophysis of the 
tibia found in the loons and grebes, but not in the auks. In auks, the elbow has two 
sesamoids. The thoracic walls are very extensive; the long jointed ribs grow all along 
the backbone from the neck to the pelvis, and form with the long broad sternum a bony 
box enclosing much of the abdominal viscera as well as those of the chest, perhaps to prevent 
their undue compression under water. The top of the skull has a pair of crescentic depres- 
sions for lodgment of a large gland; the palate is schizognathous. The sternum has a 
different shape in each of the families. There are two carotids, except among the grebes, 
and in Alle. The digestive system shows minor modifications, but accords in general with 
the piscivorous regimen of the whole order. The sexes are alike; the young different; the 
seasonal changes often great. The auks are altricial, the loons and grebes precocial. 
There are three families of Pygopodes, sharply distinguished by external characters ; all of 
them are fully represented in this country, where all the known species of loons and auks 
occur. The penguins (Spheniscomorphe), formerly included in this order, are better left, to 
stand by themselves; they are confined to the Southern Hemisphere, where they are represented 
by several genera (as Aptenodytes, Pygoscelis, Hudyptes and Spheniscus) and about 13 species. 
-The wings are reduced to mere flippers, without true remiges, unfit for flight, but very efficient 
as fins in swimming under water. Much of the plumage is harsh and scaly. There are numerous 
osteological characters, among them the flatness and solidity of the wing-bones, and the incom- 
plete fusion of the metatarsals. The elbow has a pair of sesamoids, and the knee a large 
irregularly shaped patella. The feet are four-toed, and palmate. 
Analysis of Families. 
Loons, Feet 4-toed, palmate . . 1... ee ew te ee ee ht we ee CoLYMBIDZ 
Grebes, Peotd-toed, lobate 42 4 «6 sa We eR EAE eee eR ew . PopiciIrpEDIDZ 
Auks. Feet 3-toed, palmate. . . 1. 1. 1 ee ee ee th tee ee ee ew ee . ALCIDE 
