14 A FIRST CHAPTER 
Phyla are divided into Classes! whose many (often thousands) mem- 
bers are constructed on the same general plan. The mammals, for ex- 
ample, have hot blood, a four-chambered heart, and suckle their young; 
all birds have feathers; reptiles have cold blood and are never clad ia 
either hair or feathers. But while these are very apparent differences 
they are associated with others, equally important if not so obvious, 
which can be expressed only in technical language. 
Classes in turn are divided into Orders? which embrace one or sev- 
eral Families. Thus the cats so closely resemble one another in struc- 
ture that all living and many extinct species are included in the family 
Felide, whose most evident character is the great development of the ca- 
nine teeth, the reduction in number of the jaw teeth and the adaptatioa 
of a few of them for cutting flesh; whence these teeth are called secto- 
rial tecth. 
Another familiar order is that containing the gnawing animals, or ro- 
dents, known as Glires. This contains more species and individuals 
than any other order of mammals, a large proportion being included in 
the well kaown family Muride that embraczs the rats and mice. 
Related families are the Hystricide or PonOUEORS Dipodide, jer- 
boas, and Sciuride or squirrels. 
The order Bruta contains those stupid, brutish creatures the sloths, 
anteaters and armadillos. It has also been termed Edentata, or tooth- 
less, some of the members lacking teeth altogether, while all agree in 
being destitute of front or incisor teeth. To the Ungulata, or hoofed 
quadrupeds, in whose ranks are found the deer, Cervide, belong also the 
sheep, goats aud cattle of the family Bovide and the horses or Equide. 
The dogs form the family Canidae, the bears the Urside, these, with 
several others, being embraced in the order Fere, known also as Carnivora 
or flesh eaters—the beasts of prey—which contains those animals not 
merely adapted for a predatory life, but agreeing in some important char- 
acters of teeth and skeleton. The mere fact that any animal is a flesh 
eater does not make it a member of the order Fere, any more than living 
in the water makes a creature a fish, for habits are not characters, al- 
though they may be characteristic. Some of the Marsupials, or pouched 
mammals, are flesh eaters and prey upon other animals, but they are 
very different from the true carnivores. While whales live in the water 
they breathe air by means of lungs, and not by gills, their blood is 
warm, their young are born alive and are nourished on milk, their back 
1Latin classis, a class. | f ; : 
2Latin ordo, a row or series, hence an order is a series of animals. 

