Analyze the distinguishing features of Class Mammalia.
a. A unique characteristic is the presence of milk-producing mammary glands.
b. The skin of mammals is unique in possessing hair.
c. External ears or pinnae are present.
d. Different types of teeth are present in the jaw.
e. The heart is four-chambered, and they are homoiothermous.
f. Respiration is by lungs.
g. All mammals are viviparous.
h. Development is direct.
