290 THE STRUCTURE AND LIFE OF BIRDS cHap. 
its claw. But the most wonderful point of all is that 
the three outermost primaries havetheir growtharrested 
while the others advance in length; later on: they 
grow to their full size. This can be well seen in the 
series of young chickens in the hall at the South 
Kensington Museum. And so the chicken, a thor- 
oughly modernized relative of the archaic Hoatzin, 
still retains this queer trace of its ancient life. 
The anatomy and habits of Hoatzin may help us to 
understand what may have been the manner of life of 
Archeopteryx. Mr. Pycraft suggests that it used its 
claws mainly during its infancy. May it not also have 
had recourse to them when moulting? A poor flyer 
at best, and its leg-muscles possibly weak, it might 
well, when bereft of some of its big feathers, or, 
through an imperfect system of moulting, bereft of 
all at once, appreciate fully the value of wing-claws, to 
help it to climb out of the reach of reptile enemies. 
We will now pass on to a comparatively common- 
place subject. As a rule a young bird differs in 
plumage from a mature one. The cock bird as he 
grows up often puts on fine plumes unknown to his 
youth. If there is a difference in brightness between 
the old birds and the young, it is always the latter 
which are characterised by ‘the more sober dress. 
But beyond this it is impossible to find a rule that will 
apply to all. When the cock is more conspicuous 
than the hen, the young usually resemble the mother. 
The young cock Blackbird, however, is easy to dis- 
tinguish in the nest by his darker tint. In the Painted 
Snipes and the few other species in which the female 
bird is more gaudy than the male, it is the latter that 
