Science, Life Science

Grade 3- 5

Objective

Students learn about eyes and eyelids that are uniquely characteristics of reptiles and amphibians.

Directions

Introduce to students the fact that many reptiles and amphibians have eyes that are different from those of mammals. Describe to them the following examples and draw pictures on the board to illustrate.
Most lizards and skinks have round pupils and moveable (closing) eyelids. The Burrowing skink has a unique clear eyelid window in its lower lid. When it closes its eyes it can still see through the bottom lid, yet keep out dirt and debris. Ask students if they can think of reasons why a burrowing skink would need to see out of its lower lid at all times.
Nocturnal geckos have vertical-elliptic pupils, while diurnal (daytime feeding) geckos have round pupils. Most geckos do not have moveable eyelids. Their eyes are always open. A transparent scale called a spectacle protects each eye. Can students think of ways that having their eyes open all the time helps geckos to survive?
Snakes' pupils are round and vertical-elliptic. They have no eyelids. They also have spectacles. The pupil shape of a snake's eye is not an indication of the presence of poison.
Most frog families have horizontal-elliptic pupils, the exception being the Burrowing and Spadefoot toad families, which have vertical-elliptic pupils. The bottom eyelids of frogs move upward and cover the entire pupil area. Can students think of reasons for this?
Crocodilians have vertical-elliptic pupils with three moveable eyelids per eye: a semi-transparent lid, the upper lid, and the lower lid. Ask students if they can think of ways that having these types of eyelids helps a crocodilian to find its prey.
Tell students that they will be completing a simulation to show an example of crocodile eyes. Distribute copies of the Crocodilian Three-way eyelid activity sheet. Students should follow the directions to complete a model of a crocodilian eye.

Resources

• transparent plastic wrap
• scissors
• tape
• Crocodilian Three-way Eyelid Action activity sheet (one per student)
• The World's Most Spectacular Reptiles and Amphibians by William Lamar (World Publishing, 1997)