268 THE SCIENCE OF LIFE. 



which is the largest cavity of all to store the food and 

 mix it with the water it contains, and which in Camels, 

 Llamas, and Dromedaries contains pits closed by mus- 

 cular rims for storing up fluid when the animal is going 

 a long arid journey ; the reticulum, or honey-comb apart- 

 ment, where the food is made into small round pellets, 

 to be regurgitated into the mouth, where they undergo 

 a second mastication ; the manyplies, with its mucous 

 membrane arranged in parallel folds, like the leaves of a 

 book, and where some digestion of soluble parts of the 

 food may occur ; and the rennet, or true digestive stom- 

 ach, where the albuminous principles of the food are 

 extracted and absorbed by the veins. 



The digestive canal is much longer in herbivorous than 

 in carnivorous Mammals, being thirty times the length 

 of the animal in the sheep, and five times the length in 

 the cat and dog. 



An external ear is rarely absent ; the eyes are always 

 present, though rudimentary in some burrowing animals; 

 and, while in all other animals the embryo is developed 

 from the nourishment contained in the egg, in Mammals 

 it derives its support, almost from the beginning, direct- 

 ly from the parent, and, after birth, is sustained for a 

 time by the milk secreted by the mammary glands. 



Order I. Monotremata. Includes two singular forms, 

 the Duck-mole, (Ornithorhynchusl) arid Spiny Ant-eater, 

 (Echidna?) both confined to Australia. The former has 

 a fur covering, a bill like a Duck, and webbed feet. The 

 latter is covered with spines, has a long, toothless snout, 

 like the Ant-eaters, and the feet are not webbed. Both 

 burrow, and feed upon insects. 



