292 THE STRUCTURE AND LIFE OF BIRDS  cuap. 
and neck. The young bird is blackish, speckled with 
white, and at each moult some of the incorrect feathers 
are weeded out. These changes, it is believed, give a 
rapid recapitulation of the history of the Gannets. At 
one time they had throughout their lives these blackish 
feathers ; in the course of generations they attained to 
their present spotless white. It is probably not till 
the fifth autumn that the plumage reaches the per- 
fection of maturity, and the next spring the bird 
makes his first nest. In the photograph at South 
Kensington of Gannets sitting on their eggs, there is 
apparently not one whose plumage shows any sign of 
immaturity. The youth of a Golden Eagle lasts ten 
years, or even longer. The rate of mortality is great 
among young birds, and but few Golden Eagles, prob- 
ably, survive to build a nest and rear young. And 
this leads us on to the subject of the age attained by 
birds, for there is no doubt that there is a connection 
between this and the age of maturity. There is a good 
deal of evidence that Eagles and their allies live to a 
great age—to 100 years and more ; and even if parti- 
cular cases are doubtful, yet on the principle that a 
number of weak sticks make a strong faggot, I think 
we may accept it. Suppose that an Eagle lives to 
only sixty years, and becomes mature at ten, then a 
pair will produce 100 eggs in the fifty years, the 
number laid being usually two, and of the hundred 
birds hatched only two will live to grow up. This 
calculation, which I quote from Professor Weissmann, 
even if only roughly correct, is valuable as bringing 
together three facts which must be viewed in con- 
nection—(1) the great length of an eagle’s natural 
