436 APPLIED BIOLOGY 



Chapman's "Bird Life" is an excellent introduction to 

 bird study. There are many good books specially adapted 

 for identification of birds in given localities. 



MAMMALS 



359. Characteristics. Mammals (Mammalia) are the 

 animals which in popular language are termed "quadrupeds" 

 or " beasts." They are sharply distinguished from all other 

 vertebrates by three characteristics : (1) milk-glands or 

 mammary glands for supplying food to the young (the 

 name " mammal " refers to this peculiarity) ; (2) true hair 

 composed of overlapping scales or dry cells ; and (3) a dia- 

 phragm dividing the body-cavity into an anterior (tho- 

 racic) cavity with heart and lungs, and a posterior (abdomi- 

 nal) cavity. No other animals have these characteristics, 

 and by applying them we can quickly decide that whales are 

 mammals and not fishes, and that bats are not birds; for 

 both whales and bats have milk-glands, hair, and diaphragm. 



360. Groups of Mammals. It is easiest to learn the 

 chief groups of mammals by reference to well-known examples 

 such as one may see in any zoological garden, menagerie, 

 or natural-history museum. In citing examples below, the 

 plural (e.g., kangaroos) is used in most cases where more than 

 one species is well known under the same popular name. 



There are about 2400 species of living mammals, and over 

 3000 extinct species. 



Orders of Mammals 



1. Monotremata (monotremes) Australian duck-bill and spiny 



ant-eater. Lowest mammals. Oviparous. All higher mam- 

 mals are viviparous. 



2. Marsupalia (marsupials) opossums, kangaroos, wombats, and 



bandicoots. The skin on ventral side of abdomen forms a 

 pouch (marsupium) in which the very weak young are carried. 

 About 180 living species are known. 



