386 SYSTEMATIC ZOOLOGY. 



of the ancient Peruvians; while in Asia and Africa the 

 camels, in part, take their place. Two kinds of camels 

 occur, one with one and the other with two humps upon 

 the back. These humps are merely large masses of fat. 

 Some fifty years ago the United States Government intro- 

 duced some camels into our southwestern territory, and 

 the descendants of these are still to be found in Arizona. 



We associate together under the common name of deer 

 all those ruminants which have horns consisting of solid 

 bone. These horns are annually shed and grow out anew 

 each year, usually increasing in size with the age of the 

 animal. When first formed the horns are covered with a 

 thin skin with short hairs. The horns in this condition 

 are said to be 'in the velvet.' When the horn is fully 

 formed the skin dies and is worn off. In some deer horns 

 are borne only by the male, but sometimes both sexes, as 

 with the reindeer, are provided with them. The long- 

 necked giraffes are closely related to the deer. 



In other ruminants the horns are never shed. In these 

 the horns consist of a central core of bone, covered on the 

 outside with a horny structure in reality modified hair 

 (p. 364). Here belong our domestic cattle, which are 

 believed to have arisen from four different species, which 

 formerly were wild in Europe. This wild stock is almost 

 extinct. One of these forms at least was closely similar to 

 our American bison, which has so nearly approached ex- 

 tinction from the desire for 'buffalo' robes. The true 

 buffalo are all natives of the Old World, and occupy a 

 position between the ancestors of domestic cattle and the 

 long series of forms grouped together as antelope, most of 

 which belong to Africa, but which are represented in 

 America by the prong-horned antelope of our western 

 states (fig. 172) which forms the sole exception to the 



