"What frightful creatures!" cried Lucien. "I can't think why the nasty
smell does not drive them away."

"It is just the reverse; it is the smell which attracts them," I
replied. "Even when they are soaring high up in the sky, and scan the
horizon with their yellow eyes, their subtle sense of smell enables them
to catch the effluvia of the putrefied matter on which they feed."

In some of the towns of Mexico the black vultures are so
numerous--living there, as they do, almost tame in the streets--that our
young companion was well acquainted with these birds; but he had never
been present at one of their joint meals. The sight of one of their
bare, black, and wrinkled necks, plunged into the body of the animal,
made him almost ill.

"Poh!--what disgusting birds!" he cried.

"You are wrong," I said; "the birds are only obeying the instinct
implanted in them. Henceforward you will understand better the name of
the 'rapacious order' or 'birds of prey,' which is given by naturalists
to vultures, eagles, falcons, and owls. You are aware that the science
which describes the habits of birds is called _ornithology_. Cuvier, the
great classifier, divides the feathered tribe into six orders--birds of
prey, passerines, climbers, gallinaceans, wading, and web-footed birds.
In order to prevent confusion, the orders have been subdivided into
families, the families into groups, the groups into genera, and the
genera into species."

"How are they all to be recognized?"

"By the study of certain special characteristics, which serve as
distinguishing marks. Birds of prey, for instance, have curved beaks and
claws, legs feathered either to the knee or down to the foot, three toes
in front, and one behind; also, the back and inside toe are stronger
than the others. The vultures which you are looking at, the only
birds of the order which live in flocks, belong to the _Cathartus_
genus."[L]

[Illustration: "A flock of vultures attracted our attention."]

"Look! there are some which keep at a distance. They look as if they
were afraid."

"No; they have gorged themselves, and are now digesting their meal;
unless danger compel them to take flight, they will remain motionless
until sunset."

"Will they attack live creatures?"

"Very rarely; for they are dreadful cowards, and, besides, do not care
much for fresh meat."

We had now left far behind us the miserable crew of carrion-eaters, when
Lucien suddenly cried out--

"Oh, pap