"PLEASED WITH A FEATHER." 369 



itself. But perhaps it is premature to build with any confidence upon 

 such dubious ground ; and we may consequently accept the earliest 

 birds on their oavu responsibility, without inquiring too curiously into 

 their antecedents, or compelling them to produce a genealogical table 

 of their ancestry. 



The essential characteristic of a bird consists in the fact that it is a 

 flying animal ; and feathers are the kind of skin-covering best adapted 

 to its special manner of life. In their nature and mode of develop- 

 ment, feathers closely agree with the hair of mammals ; but the dif- 

 ferences between them are all of a sort which fit the bird for its aerial 

 existence. We see this fact very clearly if we look at the instance of 

 those birds which do not fly. Running species, such as the ostriches, 

 have downy plumes, in which many of the essential characters of the 

 feather are greatly obscured. In the emu, whose habits are more 

 strictly cursorial, the plumage almost resembles hair. In the casso- 

 wary the likeness becomes yet more striking, while the wingless 

 apteryx of New Zealand has not even the few bare quills which stand 

 for wing-feathers in the former bird. So, too, among those sedentary 

 marine birds, the penguins, where the wings have been converted into 

 a sort of fins for diving, the feathers undergo a parallel change into 

 scales. There is reason, indeed, to suspect, as Mr. Lowne has pointed 

 out, that these marine species retain in many ways the primitive char- 

 acters of the class ; and we may perhaps regard them rather as birds 

 in whom the pinions and plumage have never fully developed than as 

 birds in whom they have assumed a new form. 



On the other hand, the truest feathers that is to say, those which 

 exhibit the essential features of a feather in the most marked manner 

 are specially connected with the act of flight. The general surface 

 of the body is covered with soft down, among which sprout the deli- 

 cate plumes that form the common covering for warmth and protec- 

 tion ; but only on the wings and tail do those long and stiff quills 

 aj)pear which, after all, are the feathers par excellence, the models and 

 prototypes of all the rest. Now, it is quite obvious to every one that 

 the wings are the organs of flight, and that the quills are the part by 

 means of which the powerful muscles of the bird are brought to bear 

 upon the sustaining atmosphere. As for the tail, its functions resem- 

 ble those of a rudder, in directing the course of flight to right or left. 

 The difference between these true flying feathers and the mere clothing 

 of the back and breast is so striking that naturalists have given them 

 separate technical names, as quills and plumes respectively. 



From such facts, and others like them, I think we may arrive at an 

 important conclusion that feathers have been developed and selected 

 through the habit of flight. Probably our monstrous friend the ptero- 

 dactyl had only a membranous wing or bit of skin, extending from the 

 elongated outer finger of his forearm to the leg. Such a parachute we 

 still see among the so-called flying-squirrels and lemurs ; while in the 

 vol. xv. 24 



