were connected in networks.
Machines called routers were invented to
connect the networks. This is how the
original ARPANET eventually grew into
the Internet.
In 1989 hypertext was invented. Hypertext
is a link between different parts of
an electronic document or between different
documents. Hypertext became the
basis of the WorldWideWeb, or “the
Web,” which was created in the early
1990s.
Information on theWeb is arranged in
sites or pages. People view Web sites
using computer programs called Internet
browsers. People createWeb sites using a
code called hypertext markup language,
or HTML. Browsers read HTML and
allow people to viewWeb sites on the
computer. EachWeb site has its own
Internet address, called a uniform
resource locator, or URL.
Since its beginnings, the Internet has
changed to keep up with the demands of
its users. Advances in technology make
using the Internet quicker and easier.
And as more and more people use the
Internet, the quantity of information
grows.
#More to explore
Computer • Technology and Invention
Intestines
Intestines are organs, or body parts, that
are shaped like long tubes. They help
break down food so that the body can
use it for energy. This is part of the process
called digestion. The intestines also
remove wastes from the body. Mammals,
birds, reptiles, amphibians, and
fish have intestines.
A human’s intestines fill much of the
middle part of the body below the rib
cage. The intestines are divided into two
main sections, the small intestine and
the large intestine. The small intestine is
22 to 25 feet (6.7 to 7.6 meters) long
and coils like a maze. The large intestine
is 5 to 6 feet (1.5 to 2 meters) long. The
intestines have a special kind of muscle
that squeezes and relaxes in a wavelike
A family uses a computer with a camera
attached to it. The camera can take pictures
that can be sent over the Internet to other
family and friends far away.
142 Intestines BRITANNICA STUDENT ENCYCLOPEDIA
motion. This motion pushes food and
waste through the intestines.
The Small Intestine
Food enters the small intestine after it
leaves the stomach. At this time the food
is in the form of a thick liquid. Digestive
juices from other organs, including the
pancreas and the liver, enter the small
intestine. They work with juices from
the small intestine to break down the
food into simple chemical substances.
These substances then pass into the
bloodstream through the walls of the
small intestine. This process takes three
to six hours.
The Large Intestine
Any food material that cannot be used
by the body passes from the small intestine
into the large intestine. The large
intestine takes water and some minerals
from this leftover food material. Tiny
living things called bacteria in the large
intestine help to turn the food material
into feces, or solid waste. The feces are
stored in the large intestine until they
pass from the body. The work of the
large intestine takes between 10 and 20
hours.
#More to explore
Digestive System • Stomach
Inuit
#see Eskimo.
Invention
#see Technology and Invention.
Invertebrate
An invertebrate is an animal without a
backbone. (An animal with a backbone
is called a vertebrate.) Invertebrates live
in every part of the world. In fact, most
of the animals on Earth are invertebrates.
Invertebrates come in all different shapes
and sizes. Some are so tiny that they can
be seen only through a microscope. But
the giant squid is an invertebrate, and it
can grow to a length of 65 feet (20
meters).
The simplest animals are invertebrates.
These include protozoans with just one
cell as well as sponges and other simple
animals that live in the water.
In humans, the small intestine is longer and
narrower than the large intestine.
BRITANNICA STUDENT ENCYCLOPEDIA Invertebrate 143
The invertebrate animals can be grouped
according to their features. Many of
them, such as worms, have soft bodies.
Corals, jellyfish, and sea anemones are
invertebrates that have stinging tentacles.
Mollusks have soft bodies as well,
but most also have a thick outside shell.
Oysters and snails are mollusks. Squid
and octopuses are also mollusks even
though they do not have shells.
Some invertebrates have a tough, spiny
skin that protects their bodies. These
invertebrates are called echinoderms.
Starfish and sea urchins are examples of
echinoderms.
Other invertebrates have a hard outside
covering on their bodies called an exoskeleton.
These invertebrates are called
arthropods. Arthropods include insects,
spiders, centipedes, millipedes, and crustaceans
such as lobsters and crabs.
#More to explore
Vertebrate
Iowa
The Native Americans known as the
Iowa (or Ioway) once lived near the
Great Lakes. By the 1700s, however,
they had moved to what is now the state
of Iowa. The state was named after the
tribe.
The Iowa lived in villages of domeshaped
houses covered with earth. They
grew corn, beans, and squash. They also
hunted bison (buffalo) and deer. After
getting horses in the 1700s the Iowa
covered greater distances while hunting
on the Great Plains. On the hunt they
lived in tepees covered with bison hides.
