READING THE RIDDLES OF THE ROCKS 107 



feathers of a water-fowl would be thick and close; 

 those of strictly terrestrial birds, such as the ostrich and 

 other flightless forms, lax and long. These are general 

 propositions; of course, in special cases, one might easily 

 come to grief, as in dealing with birds like penguins, 

 which are particularly adapted for an aquatic life, and 

 have the feathers highly modified. These birds depend 

 upon their fat, and not on their feathers, for warmth, 

 and so their feathers have become a sort of cross be- 

 tween scales and hairs. Hair and fur belong to mam- 

 mals only, although these creatures show much variety 

 in their outer covering. The thoroughly marine whales 

 have discarded furs and adopted a smooth and slippery 

 skin, 1 well adapted to movement through the water, 

 relying for warmth on a thick undershirt of blubber. 

 The earless seals that pass much of their time on the 

 ice have just enough hair to keep them from absolute 

 contact with it, warmth again being provided for by 

 blubber. The fur seals, which for several months in the 

 year dwell largely on land, have a coat of fur and hair, 

 although warmth is mostly furnished, or rather kept in, 

 by fat. 



No reptile, therefore, would be covered with feathers, 

 neither, judging from those we know to-day, would they 

 be clad in fur or hair ; but, such coverings being barred 

 out, there remain a great variety of plates and scales to 

 choose from. Folds and frills, crests and dewlaps, like 



J The reader is warned that this is a mere figure of speech for, of 

 course, the process of adaptation to surroundings is passive, not active, 

 although there is a most unfortunate tendency among writers on evo- 

 lution, and particularly on mimicry, to speak of it as active. The 

 writer believes that no animal in the first stages of mimicry, consci- 

 ously mimics or endeavors to resemble another animal or any part of 

 its surroundings, but a habit at first accidental may in time become 

 more or less conscious. 



