Page 211 - Biology_F5

Biology for Advanced Level Secondary Schools

the hind end of the trunk is the cloaca aperture.

Eye Neck
Beak
(bill)
Wrist Contour feathers
FOR ONLINE READING ONLY

Greater wing coverts
Flight feathers on tail
Tibia
Finger digit
Claw
Figure 3.71: Structure of a pigeon

Distinctive features of the class Aves (h) Their alimentary canal has additional
Aves differ from other chordates due to chambers called crop and gizzard.
possession of the following features: The crop stores and softens the food,
(a) Their bodies are covered by overlapping while the gizzard helps in crushing and
feathers. churning the food.
(b) They lost teeth; instead, they have (i) Birds are capable of flying except for a
modified mouthparts to form different few species such as ostrich, penguins,
types of beaks (bills). Beaks are adapted kiwi, emus, rheas, and cassowaries.
for many different feeding habits, such Flightless birds are characterised
as seed crushing, fruit scooping, flesh by the absence of a keeled sternum
tearing, nectar sipping, and wood (breast bone), which is necessary for
chiseling. the attachment of flight muscles.
(c) They have long, cylindrical necks
connecting heads and trunks. Class Mammalia
The class Mammalia consists of all animals
(d) They have two pairs of pentadactyl limbs. with mammary glands. It is an extremely

The front limbs are modified into a pair diverse and very advanced group in the
of wings, which bear quill feathers for kingdom Animalia. Members of the class
flight, while the hind limbs are covered Mammalia include: human, mouse, rabbit,
by scales and are adapted for perching, cattle, lion, bat, whale, and donkey.
walking or swimming.
Distinctive features of class Mammalia
(e) They undergo internal fertilisation and Mammals are different from other chordates
produce eggs with calcareous shells. because:
(f) Their sternum forms a sharp ventral keel, (a) They have fur or hair that cover their
providing muscle attachment for flight. skin. The skin is glandular, with two
types of glands, namely sebaceous and
(g) They have oil gland above the cloaca, sweat glands.
which preens the feather so that they (b) They have mammary glands, which
become waterproof. Ostrich and parrot produce milk for their newborn in
lack oil gland. females.

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