After enlisting the help of thousands of volunteers to track how digital information weaves around the world, researchers can offer a new simile: The Internet is like a medusa jellyfish. It has a dense core surrounded by a highly connected body, from which tentacles dangle.
Because the Internet has grown haphazardly, its structure has been mysterious. It began when universities, government agencies, and a few companies linked their internal computer networks to share information. New groups have kept joining ever since, with no central authority organizing the process. An e-mail sent today may pass through as many as 30 subnetworks before reaching its destination.