METHODS OF PROTECTION AMONG ANIMALS. 159 
of the “ periostracum” or “overcoat” of certain mollusca, 
to which reference has been made. Though not strictly 
protective structures, the air-sacs found in the bones 
of a great many birds may be looked upon as indirectly 
protective by reason of the warming effect upon the air 
of respiration, acting as a reserve warm-air chamber, which 
is of value to the bird in its rapid inspiration of cold air, 
The beaks of birds confer necessarily protection upon 
them, as teeth do in other animals. The skull is welded 
together into one solid, light, strong bone in adult birds, and 
lightened by air spaces. 
The nasal passages are protected by the position of the 
apertures, placed far back on the skull. The external ears 
are carefully protected by a tuft of hair. 
The eyes of birds are specially protected by the “ third 
eyelid,” or “membrana nictitans,” also highly developed 
in fishes, and much less in some mammalia. In birds and 
fishes this movable mucous membrane is of obvious 
advantage in protecting the eyeballs against the impact of 
foreign bodies in the air and water. It is capable of being 
rapidly moved across the eyeball, serving in the most. 
beautiful manner to protect, lubricate, and cleanse the 
surface. 
It remains only to mention the names of the leading 
members of this great class of highly specialized animals, 
and such of them as are familiar will at once suggest to 
our minds modifications of the protective structures given 
above. Lyddeker enumerates them as follows :— 
Perching Birds, Woodpeckers, Cuckoos, Hornbills, Parrots, 
Owls, Ospreys, Eagles, Falcons, Vultures, Pelicans, Cormorants, 
Gannets, Storks, Herons, Flamingoes, Ducks, (Geese, Swans, 
Screamers, Pigeons, Dodos, Sand-qrouse, Fowls and Game birds, 
Rails and Coots, Cranes and Bustards, Plovers, Curlews, Snipe, 
Gulls, Terns, Albutrosses, Petrels, Divers, Auks, Penguins, 
Tinamus, Ostrich, Emu, Cassowaris. 
Among the great class of mammalia those characters. 
conferred upon them for protection present to us a broad 
fact strikingly illustrative of design. This class includes 
animals of a higher organization in almost all respects than 
those that have preceded. Of these the most important is 
higher cephalizution or increasing proportion of the size 
and complexity of the brain. In lower levels of life there 
are some remarkable exceptions to this broad rule, eg., 
among insects the brains of an ant so impressed Darwin 
