PTERYLOSIS OF BIRDS 



that the feathers are disposed in definite tracts, whose 

 arrangement varies from bird to bird, and often affords 

 valuable evidence of affinity : between these tracts are 

 either naked spaces or spaces sparsely covered with scat- 

 tered small feathers. The penguin, on the other hand, 

 has a " pterylosis," which is continuous all over the body, 

 save, as it appears, for a small region on the under 

 surface, which is pressed upon the eggs when the bird 

 is sitting on its nest. In this way the eggs get more of 

 the heat of the body ; for, as is well known, feathers are 

 bad conductors of heat, and are thus useful for keeping 

 a bird warm, and us when we use feather muffs, duvets, 

 etc. It is a remarkable fact that this little bare patch 

 only occurs in the female, and yet both sexes sit upon 

 the eggs. Perhaps it argues that the share of the 

 father in the well being of his offspring is only a recent 

 occurrence, and that formerly the hen alone performed 

 this important function. This feathering of the pen- 

 guin is supposed by some to indicate the retention of 

 an archaic character. And if the feathers of a bird 

 may be derived directly from the scales of some reptile 

 forefather, an uniform feathering would naturally be 

 the original condition. Speaking of the scales of some 

 reptilian ancestor, it is a most noteworthy fact that the 

 difference between a scale and a feather is reduced 

 to an apparently irreducible minimum in the paddle. 

 Flat, closely depressed and unbarbed " feathers " cover 

 that member, and it was discovered by the late Mr. 

 A. D. Bartlett that the skin of the fore arm is shed 

 in a piece, like the skin of a snake, instead of being 

 moulted in bits like the feathering of a fowl. Another 

 ancient character (at least in the opinion of some), 

 which the penguin shows is the fact that the three 

 bones in the foot known as the metatarsals, those 

 bones which lie between the ankle and the commence- 

 ment of the bones of the toes, are slightly separated 

 Z.G. 225 Q 



