PYGOPODES, DIVING BIRDS. 333 



auks and penguins, lobate with basal webbing in the grebes ; the hallux is present 

 and well formed, with a membranous expansion, in loons and grebes, very minute 

 and lateral in position in the penguins, wanting in the auks. The plumage is thick 

 and completely water-proof ; once observing some loons under peculiarlj' 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 ; in the penguins the feathers are implanted evenly over the whole skin ; in 

 the rest 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 (fig. 8) and grebes, but not in the auks 

 and penguins : in the latter, the patella is of great size, and it is stated to develop 

 from two centres. In penguins and auks, the elbow has two sesamoids ; among the 

 former, there is a free ossicle in the heel joint. The thoracic walls are very exten- 

 sive ; 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 depressions for lodg- 

 ment 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. 

 The digestive system shows minor modifications, but accords in general with the 

 piscivorous regimen of the whole order. The sexes are alike ; the 3'oung different ; 

 the seasonal changes often great. A part of the order are altricial, the rest 

 prsecocial. There are four families of Pygojjodes, sharplj^ distinguished b}' external 

 characters ; three of them are represented in this country. The penguins {Sphen- 

 iscidai) are confined to the seashores of the southern hemisphere. This group is 

 well marked by the solidity of the skeleton, and the flatness of most of the bones, 

 with many peculiar osseous details ; by a very special ptilosis, both in the lack of 

 tracts, and the structure of the feathers themselves, many of which are curiously 

 scale-like ; by the completelj' posterior set of the legs with extremely short tarsus, 

 and especially, among external features, b}^ the reduction of the wings to mere 

 paddles, lacking specially formed remiges, unserviceable for flight, but highly 

 efficient as fins to aid progress under water. There are twelve species of penguins, 

 referable to three or four genera. One of the most singular facts in ornithology is, 

 that some species of penguin do not \&y their egg in a nest in the ordinary way, 

 but carry it about with them in a pouch temporarily formed by a fold of the 

 abdominal integument (Ferrecraa;) ; thus affording a wonderful analogj^ to marsu- 

 pial mammals. The author's monograph of the SpJieniscidce will be found in the 

 Proceedings of the Philadelphia Academy, of the present year. 



Family COLYMBID-aE. Loons. 



Bill stout, straight, compressed, tapering, acute, paragnathous, entirely hornj'. 

 Nostrils narrowly linear, their upper edge lobed. Head completely feathered, the 

 antiaj prominent, acute, reaching the nostrils ; no crests nor ruffs. Wings strong, 

 with stiff primaries and short inner quills. Legs completely posterior, buried, 

 feathered on to the heel-joint ; tarsi entirely reticulate, extremely compressed, the 

 back edge smooth ; toes four, the anterior palmate, the posterior semilateral and 

 having a lobe connecting it with the base of the inner. Tail short, but well formed, 



