484 
PLimr^S NATURAL HISTOHT. 
[Book X. 
with its wings, and forces them from time to time to look 
steadily upon the rays of the sun ; and if it sees either of 
them wink, or even its eye water, it throws it headlong out 
of the nest, as being spurious and degenerate, while, on the 
other hand, it rears the one whose gaze remains fixed and 
steady. The haliaetus is not a species of itself, but is an 
eagle of mixed breed : hence their produce are of the species 
known as the ossifrage, from which again is produced the 
smaller vulture; while this in its turn produces the large 
vulture, which, however, is quite barren. 
Some writers add to the above a seventh kind, which they 
call the " bearded "^^ eagle ; the Tuscans, however, call it the 
ossifrage. 
CHAP. 4. THE NATURAL CHARACTERISTICS OF THE EAGLE. 
The first three and the fifth class of eagles employ in the 
construction of their aerie the stone aetites,^^ by some known 
as gangites which is employed also for many remedial 
purposes, and is proof against the action of fire. This stone 
has the quality also, in a manner, of being pregnant, for when 
shaken, another stone is heard to rattle within, just as though 
it were enclosed in its womb ; it has no medical properties, 
however, except immediately after it has been taken from the 
nest. 
Eagles build among rocks and trees ; they lay three eggs, 
and generally hatch but two young ones, though occasionally 
as many as three have been seen. Eeing weary of the trouble 
of rearing both, they drive one of them from the nest : for 
just at this time the providential foresight of I^ature has denied 
them a sufficiency of food, thereby using due precaution that 
the young of all the other animals should not become their 
prey. During this period, also, their talons become reversed, 
and their feathers grow white from continued hunger, so that 
it is not to be wondered at that they take a dislike to their 
26 See Lucan, B. ix. 1. 902. 
He contradicts himself, for he has already stated that it is the sixth 
species. 
28 " Barbata.'* Cuvier takes it to he the laemmer-geyer, or G}^aetus, 
the only bird of prey that has a heard. 
29 Or eagle-stone. See B. xxxvi. c. 39. He does not there mention 
that it is combustible. It is not impossible that pieces of aetites, or ferru- 
ginous geodes, may have been found in an eagle's nest. 
