284 



Descriptive Zoology. 



CLASSIFICATION OF MAMMALS. 



SUBCLASSES. 

 i. Prototheria . . . 



ORDKRS. 



i. Monotremata Duckbill and Spiny Ant-eater 



f (Nonplacentals) . 2. Marsupialia 



3. Edentata . 



4. Rodentia . 



5. Insectivora . 



6. Cheiroptera 

 -[ 7. Cetacea . . 

 I 8. Sirenia . . 

 I 9. Ungulata 



I 10. Proboscidea 

 ii. Carnivora . 



2. Theria -! (Placentals) 



Opossum, Kangaroo 



Sloth, Armadillo 



. . Rabbit, Squirrel 



. . . Mole, Shrew 



Bat 



Whale, Porpoise 

 .... Sea Cow 

 . Horse, Cow, Deer 

 . . . . Elephant 

 Cat, Dog, Bear, Si-al 



L 1^12. Primates Lemur, Ape, Man 



CHARACTERISTICS OF CHORDATA. 



1. There is a notochord, a long skeletal rod, a sort of 

 forerunner of the backbone. 



2. There are gill slits opening from the throat to the 

 outside. 



3. The central nervous system is a hollow tube and is 

 wholly dorsal to the digestive tube. 



CHARACTERISTICS OF VERTEBRATA. 



In the Vertebrata the characters given for the Chordata 

 are distinctly displayed, and a permanent backbone is de- 

 veloped. A cross section of a vertebrate shows two cavities 

 (see Fig. 150), the dorsal containing the cerebro-spinal 

 nervous system, and the ventral containing the digestive, 

 circulatory, and respiratory organs. In the vertebrates a 

 liver is always present. The nervous system is usually 

 well developed. 



Classification of Animals. An early classification divided 

 animals into two groups, the vertebrates, or the animals 

 having backbones ; and the invertebrates, those lacking a 



