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The Frog
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Background Information
Frogs a re classified as amphibians, or animals that live a double life. T he name is
appropriate because amphibians spend their immature lives in water and their adult lives
primarily on land. Tadpoles, or young frogs. are emirel�· aquatic. Adult frogs can live on
land or m water.
In this investigation you will dissect a frog.
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Problem
What are the basic external and internal structures of an amphibian? How is an adult
frog adapted to live in water as well as on land?
Mate9als (per group)
)
preserved frog
d i ssecti ng tray
d i ssecting pins
dissecting kit (scalpel. scissors.
forceps. dissecting needle.
med icine dropper. probe)
Procedure.
Part A External Features
I. Place the frog on its bellr (ventral side) in the dissecting pan.
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2. Examine the back {hindJ legs and from (fore) legs of the frog. The hindlegs are strong
and muscular and are used for jumping and swimming. The forelegs provide balance and
cushion the frog when it lands after jumping. Notice the difference between the toes of
the hindlegs and those of the forelegs. In Figure 2 in Observations, label the hindlegs
and forelegs.
3. Locate the large. bulging eves. The frog has three eyelids. The two outer ones are the
color of the frog's .body. These �pper arid lower lids do not moyc;. The third eyelid is a
transparent membrane that protects the eye while permming the frog to see under
water. It also keeps the eye moist when the frog is on land. ln Figure 2. label the eye.
� 4. Behind each eve, find the circular eardrum. Then locate the two openings into the nasal
cavity. These nasal openings. or external nares. found toward the tip of the snout, will
close' when the frog is under wat�r. In Figure 2, � the �h. eardrum. and � I
openings.
• 5. Feel the frog·s skin. It is �ooth. �st, and thin. Because the skin is thin and moist. the
frog can breathe direct!\' through its skin as well as with its lungs. Flip the frog over ro
examine its bell�·- ]\jorice the difference in coloring between the bell\·· and the rest of the
frog's body.
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