238 ZOOLOGY. 



occasionally occurs independent of any great change in the 

 colour or character of the hair ; in other animals it is diffe- 

 rent. The common squirrel, for example (Fig. 118), whose 

 fur is of a deep red in summer, becomes of a fine greyish- 

 blue tint in winter. It is at this season that the hair of 

 mammals becomes much thicker, having underneath the fur 

 in much larger quantity. Climate also plays its part in 



Fig. 196. The Pangolin (Scaly Ant-eater), or Manis. 



modifying the fur or hairy covering of the skin ; hence we 

 seek in cold climates chiefly for the skins of animals supply- 

 ing the valuable furs of commerce: Siberia and North 

 America are the true fur countries. 



When the hairs grow extremely close together, they seem 

 to become matted, and to form those horny plates covering 

 the bodies of some mammals, as the pangolins (Fig 196) and' 

 the cuirass of the armadillo. Anatomists also consider nails 

 and horn as having the same origin. 



391. The Skeleton. The general form of the body is 

 determined by the skeleton, but this must not be extended to 

 the outline in every instance ; the hump of^the camel, and the 

 dorsal fins of whales, are not supported internally by any por- 

 tion of the skeleton (Fig. 197). The skeleton presents always 

 the greatest analogy with the human, which we have already 

 studied ( 269, &c.) The differences may be reduced, 1st. 

 To the absence of the abdominal limbs in the fish -shaped 

 mammals called cetacea (Fig 193). 2nd. In the diminution 

 of the number of the fingers and toes, and the absence of collar 

 bones in those in whom the limbs serve merely as instruments 

 of progression and support. 3rd. To some varieties in the 

 number of the vertebrae, especially of the caudal. 4th, In- 

 equalities in the relative size of various bones. 



