Nature Bulletin No. 698   December 15, 1962
Forest Preserve District of Cook County
Seymour Simon, President
David H. Thompson, Senior Naturalist

****:THE SHAPES OF ANIMALS

The shape of an animal tells a great deal about the kind of life it leads. 
Unlike common plants which stay rooted to one spot, they are active 
creatures that move about under their own power. They crawl, walk, 
run, jump, climb, dig, swim or fly. They hunt food, make homes, 
produce young, flee from their enemies or fight them. Certain body 
proportions and types of legs, wings or other features go along with 
each habit of life. Animals, even when they are at rest, give the 
impression of being ready to do something or go somewhere.

For example, animals that specialize in jumping, such as the rabbit, 
frog, flea, grasshopper and kangaroo, have long powerful hind legs. The 
climbers may have the grasping feet of the opossum and raccoon; the 
hooked claws of tree squirrels, cats, woodpeckers and many insects; or 
the suction cups of the tree frog's toes, or the housefly's feet, by which 
they can walk up a window pane or upside down across a ceiling. The 
best diggers -- the mole, woodchuck, badger and the underground 
young of a 17-year cicada -- have short stout forelegs equipped with 
heavy claws for scooping earth.

However, most animals are not so highly specialized. Usually, each can 
travel in various ways and perform many different tasks. None is a jack-
of-all-trades, able to do a little of everything.

Animals have a functional beauty all their own, and we describe it with 
such words as grace, poise, rhythm, smoothness of contour, and 
symmetry -- no matter whether they are as large as a 100-ton whale or 
as small as a microscopic water flea. What flower can thrill us so much 
as a glimpse of a bounding deer, a hunting fox, a soaring hawk or 
merely small fish swirling in an aquarium?

Their charm comes from a simple basic design widespread among free-
living animal life. They have a head end and a tail end; an upper side 
and a lower side; a right side and a left side. In the higher animals the 
organs of sight, hearing, smell and taste are located in the head end. 
Animals as low as the earthworm also have a head end which leads the 
way and is sensitive to outside stimuli even though it has no eyes, ears 
or special sense organs. Animals are usually bilaterally symmetrical, the 
right side tends to be a mirror image of the left side. This balance makes 
it easier for them to steer a course and not so apt to go around in circles 
like a bird with a crippled wing.

Streamlining and speed go together. The ideal torpedo-like shape is 
seen in the whizzing flight of the chimney swift, the racing greyhound, 
the migrating salmon that fights its way upstream for hundreds of miles, 
and the porpoise which can outdistance fast ships. On the other hand, 
just as the man who runs the 4-minute mile is differently built from the 
shot put champion or the wrestler, the slow-moving animals are 
imperfectly streamlined. They may even be lopsided like the creeping 
snails or, like some of the anchored sponges, be entirely lacking in 
definite form or symmetry.

Perhaps the strangest of all transformations in shape is found among the 
marine flatfishes which include the flounders, halibuts, turbots, soles 
and others. These start life like any other young fish, swimming along 
in the conventional upright position with one eye on each side of the 
head. At an early age they begin to lean over more and more to one side 
or the other. At the same time the eye on the lower side begins to 
migrate across the top of the head, or even through the head, to the 
upper side. Some species lie on their left side, others on the right, and a 
few don't seem to care which side is up.