PRINCIPLES OF ANIMAL BIOLOGY 57 



26. Usually possess two pairs of limbs with five digits each. Examine 

 a toad, a frog, and a salamander for verification of, or exception to, this 

 rule. 



2c. Skin is without scales or other hard parts, and is slimy owing to 

 a mucous secretion. Handle a living frog to observe these features. 



2d. Young breathe by gills (observe a tadpole); adults usually 

 breathe by lungs (see dissection of a frog, also the respiratory movements 

 of a living frog). 



3. Class REPTILIA (Lat. repere = to crawl). Lizards, snakes, turtles, 

 alligators, etc. 



Characteristics. 



3a. Cold blooded. 



36. Skin possesses scales or hard plates. Observe in a snake; in a 

 turtle; in a lizard. 



3c. Body not slimy. 



3d. Breathe by means of lungs throughout life. Note the lungs, 

 in a dissection of the snapping turtle, or other reptile. 



4. Class AVES (Lat. avis = bird). 



Characteristics. 



4a Warm blooded. How does a fowl incubate her eggs? 



46. Terrestrial. Even wading and swimming birds spend the major 

 portion of their time on land. 



4c. Body covered with feathers. Examine one or more feathers 

 under a lens. Compare with figures. 



4cL Fore limbs modified as wings. Examine the skeleton of a wing 

 and note its deviations from the typical vertebrate limb. Examine also 

 the character of the feathers which add to the wing expanse, 



4:6. Absence of teeth in modern birds. Examine a bird skull. 



5. Class MAMMALIA (Lat. mamma = a breast). Man, monkeys, 

 whales, bats, seals, and many common wild and domestic animals. 



Characteristics. 



5a. Warm blooded. What is your own temperature? 



56. Mostly quadrupeds. Some, however, progress on two feet 

 (man), some by "wings" (bats). 



5c. Skin covered with hair. Observe hair in squirrels, bats, or other 

 quadrupeds; also spines in hedgehog or porcupine. 



5d. Young nourished after birth by secretion from mammary glands 

 of mother. 



C. SUBDIVISION OF THE CLASSES 



To illustrate the subdivision of the classes of animals into smaller 

 groups called orders, the Amphibia and Reptilia may be selected. There 



