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Name: Central Valley Jr. Academy
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Question:
Our class has been studying about big cats. We studied cats' eyes. We learned why cats' eyes seem to glow in the dark. The back of each cat's eyes has mirror-like cells that reflect light. We used a coffee can and some construction paper to make a model of a cat's eye. We made the pupil oval shaped like a cat's eye. We shone a flashlight in the pupil and we saw the reflection. A book that we read said that nocturnal hungers mostly have long, oval-shaped pupils and daytime hunters have round pupils. We w want to know what difference that makes to an animal in being able to see.j Why do daytime hunters have round pupils and nocturnal hunters have oval shaped pupils. Do you know why?



Replies:
I think that the reason that nocturnal hunters tend to have vertical pupils while diurnal (daytime) hunters tend to have round ones, has to do with the ability of the pupil to adjust its opening quickly. For nocturnal hunters, the pupil must open very wide to gather all available light (same reason they have reflective backs), yet they need to be able to shut down very tight in bright light. A diurnal hunter, in contrast, never really is asked to use its best vision at night, and thus does not have as much need to adjust pupil size. As to why vertical slits are easier to adjust than round pupils, it's only a guess, but I think it has to do with the mechanical forces of the muscles involved; its just easier to build a rapidly adjustable slit than a rapidly adjustable round pupil. Hope this helps.

Ethan Allen



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