CLASSIFICATION OF ANIMALS AND PLANTS 137 



order contains the opossum and kangaroo, animals with a 

 pouch for carrying the young. Now, all these animals have 

 certain common characteristics. For example, a cow, dog, 

 rat, and kangaroo all have hair, all feed their young with 

 milk, and all have a diaphragm for breathing. None of these 

 important things is found in birds, frogs, fishes, worms, and 

 other low animals. Hence the animals which have these 

 characteristics are considered related in one large group. 

 And to such a group of orders the name class is applied ; and 

 the particular class to which the flesh-eaters, the gnawers, 

 the hoofed animals, and several other orders belong is Mam- 

 malia, or mammals, a name referring to the fact that the 

 young are fed with the secretion of milk-glands or mammary 

 glands. 



126. Phyla, or Divisions. Classes in turn are united 

 into larger groups. The class Mammalia and the classes 

 to which birds, reptiles, frogs and fishes belong are all com- 

 posed of animals which have a backbone or vertebral column. 

 This larger group, which contains all animals with a back- 

 bone (fishes, amphibia, reptiles, birds, and mammals), is one 

 of the great divisions of the animal kingdom, and has long 

 been known as the phylum or division of vertebrates (Verte- 

 brata, but some authors prefer Chordata). 



Other primary divisions or phyla (plural of phylum) of the 

 animal kingdom are those represented by the shelled animals 

 (oysters and snails), by the animals with jointed legs (cray- 

 fish, lobster, crabs, spiders, insects), by the worm-like ani- 

 mals (earthworm, tapeworm, leech, etc.), by the jelly-like 

 animals (jellyfish, coral-animal), by the sponge-animals, and 

 by the simplest microscopic animals. The technical names 

 are given in 133, but for our present purpose it is sufficient 

 to state that there are about a dozen such primary groups or 

 phyla in the animal kingdom. Each such primary division 

 may be called a division, phylum, or branch ; but phylum is 

 used by most zoologists. 



