WHY DID THE BIRDS PUT ON SOFT RAIMENT? 19 
for extremes could migrate over the greatest range of 
climate, and a better development of feathers meant 
a better development of flight and the finding of 
newer and better food regions—in fact, progress gen- 
erally. They traveled on their good clothes literally 
as some persons do figuratively. It was a wonderful 
step, therefore, when the ancestors of our modern 
birds first donned soft raiment. 
It may be well before closing this chapter to 
say that, contrary to the usual popular impression, 
feathers were not given birds to make them light. 
Feathers have weight of their own, and from this 
standpoint birds would be better off without them. 
It is true that some seeds are floated in the air by 
vegetable downs, and that some spiders migrate on 
gossamers ; but there is a very small limit to these 
uses of fluffy substances—not reaching up to the 
weight of the bird, even if it were designed to float 
(only) in the air. 
It is well known that weight is necessary to actual 
flight, and, as a rule, the heaviest birds are among the 
best fliers—especially the best soarers. Even a but- 
terfly could not go against the wind if it had not some 
weight. 
There is no doubt, however, that the flight quills 
are made as light as possible consistent with stiffness 
and strength, and that the tubular form of the barrel 
(toothpick part) and pithy nature of the shaft are 
partly brought about by these demands; and doubt- 
less all the plumage is affected by these conditions, 
first set up in wing and tail. But mere lightness is 
