310 PRACTICAL LESSONS IN SCIENCE. 



The wild boar of Europe, Africa and Asia was perhaps the progeni- 

 tor of all the varieties of the domestic pig, but they are so widely 

 distributed and vary so greatly that some have thought they 

 must have originated from several sources. Besides these, there 

 are the wart hogs of Africa, the peccaries of America, and the 

 babyroussa or hog deer of Southeastern Asia. The domestic 

 pig is one of the most important food-producing animals known 

 to man. 



The Obesa, or Hippopotami, are large unwieldly amphibians, 

 vegetable eating animals, living in Southern Africa, that belong 

 in this order. 



The other members of this order are ruminants, distinguished 

 by incomplete dentition and by the peculiarities of the digestive 

 organs. The animal crops the food, and without much mastica- 

 tion it passes from the oesophagus into the paunch, where it soaks 

 in the secretions for a time, then passes to the honeycomb bag, 

 or reticulum, where it is made up into little balls and returned to 

 the mouth by regugitation. After thorough mastication, the 

 food passes to the third stomach, called " many plies " or "psal- 

 teriunii" because its lining membrane lies in many folds. From 

 this cavity the food passes with little change into the rennet 

 stomach, where the food is really digested by the secretion of the 

 peptic glands. 



The Tylopoda include the camel and dromedary of the Old 

 World and the llama, alpaca, etc., of the New. The soles of the 

 feet are covered with horny integument on which the animal 

 walks, and there is no separate psalterium. 



The Arabian camel has numerous large cells in its paunch 

 which enable it to carry several days' supply of water. The gi- 

 raffes and musk-deer belong to this order. 



The Cervidae, or deer, are characterized by a pair of solid dermal 

 horns attached to a bony process of the forehead ; they are cast 

 off and renewed from year to year, the weight and number of 

 parts usually increasing with each renewal. The red deer, the 

 stag, the elk, the reindeer, used as a beast of burden in Lapland, 

 and others, are members of this family. The deer and stag have 



