Page 22 - One Million Things: Animal Life - The Incredible Visual Guide

SYMMETRY One group of animals, the sponges, lacks any
ASYMMETRY
sort of symmetry. These simple animals grow in a
random fashion. Their asymmetric structure, cut
The bodies of most animals show symmetry in any direction, will not produce equal halves.
(balanced proportions). Some show radial
symmetry, meaning they can be divided,
like a cake, through a central point into BILATERAL SYMMETRY
From butterflies to buffalo, most animals show
two identical halves. Most animals are bilateral symmetry. This means that an imaginary
bilaterally symmetrical—they can be line drawn along their length would divide them
divided down their midline into into identical left and right halves, each with
two equal halves. Other animals front and back ends. A line anywhere else,
have features that make however, would not produce equal halves.
them look strangely
lopsided.

Blue morpho
butterfly

Head
includes
eyes, nose,
whiskers,
and mouth

Right side of flounder
is now its upper
surface

Weddell seal

HEADS
Animals that are bilaterally symmetrical have a
front end called the head. This contains the animal’s
sense organs, such as the eyes, ears, nose, and whiskers,
which meet the environment before the rest of the body. Left eye has
They detect changes, which the brain, also contained in migrated over to the
right (upper) side
the head, analyzes and responds to.
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