124 THE INFANCY OF ANIMALS 



But we can carry our evidence yet further, for there 

 seems good reason to believe that the phenomena described 

 in the hoatzin and the gallinaceous birds were at one 

 time common to all birds. At any rate birds so remote 

 as the touracous on the one hand, and the rhea, or South 

 American ostrich, and the tinamous on the other, also 

 display an arrested development of the outermost quiUs, 

 and a free finger-tip during the nestling stages ; and the 

 two last-named species have lived remote from trees for 

 countless ages ! 



The fact that similar traces of an arboreal life are rarely 

 to be met with in the precocious young of birds other 

 than gallinaceous birds is a curious and extremely inter- 

 esting point, revealing not only changes in the tactics 

 adopted for the escape from enemies, but drawing attention 

 to another, and what we may caU a second string to the 

 bow practised by the gallinaceous birds themselves. It 

 is to be remembered that these latter are reared in com- 

 paratively large families, and that they in consequence 

 afford a conspicuous and tempting bait to prowling car- 

 nivora. 



Accordingly, as soon as danger is realised by the parent, 

 the alarm-note is given and the young scatter in all direc- 

 tions. Halting at last, they then fall back upon this 

 "second string" — ^protective coloration. That is to say, 

 they have, in addition to the remarkably accelerated 

 flight, also acquired a peculiar type of plumage which 

 enables thefn to assimilate with their surroundings. Now 

 it would seem that this precocious power of flight has 

 not proved a really satisfactory method of escape, inasmuch 

 as in fleeing from immediate danger the young either 

 strayed too far to render recall possible, or they fled 

 into new dangers. Consequently the young of other 



