Charles Darwin saved his last book for animals that were, in his opinion, among the most significant in world history.
These "lowly organized creatures," as he called them in his book, are the earthworms.
Sam James, a research associate at Kansas University's Natural History Museum, likewise has a special place in his heart for worms. He's been studying the little dirt-eaters for decades.
James started in 1979, in the soils of the Konza Prairie, near Manhattan. He captured a number of specimens, then shared them with scientists at Great Britain's leading natural history museum.
He had found three new species.
Today, James is one of the few scientists on Earth naming and describing new earthworms.
For example, in a recent paper in the Journal of Natural History, James confirmed seven new species from Taiwan.
The naturalist who had found them specializes in shrimps, crabs and lobsters, so he passed them to James for identification.
But Taiwan is not where James would go to collect worms. He prefers the Philippines or Brazil.
He's confident his work will result in a tenfold increase in the number of known earthworm species in the Philippines.
How did he know to look there? A tip from a colleague. The guy had found that the diet of several Philippine mammals, including the voracious tweezer-beak rat, was 60 to 80 percent earthworms.
James says, "From two sites, this guy sent 26 species of earthworms. Twenty-five were new to science."
James quickly answers some questions about worms that have crossed most of our minds.
Take that wide band you'll see on an earthworm. It's a sign that the worm is an adult. The band's location tells you where to look for the worm's head. The band is always closer to the head than the tail.
All worms have both male and female equipment. When worms mate, both receive sperm and both eventually lay eggs.
To flush worms from the underground, James dissolves a worm irritant in water -- formaldehyde or hot mustard or wasabi powder -- and sauces the earth with the liquid.
And here come the worms.
I say to James, "You take a lot of kidding, don't you?"
He says, "You've got to have a sense of humor. I'll tell you the answers to some of your other questions in advance.
"No, I've never eaten a worm.
"No, I'm not in the business of buying or selling them.
"No, if you cut a worm in half, you don't get two worms."
James says there's one other worm person in this country who does species descriptions, a few in Europe and Asia, one or two in Africa.
The eight or 10 folks in this line of business do gather occasionally to swap information and stories.
James, for example, can tell them about a foot-long indigo-colored worm in the Philippines. It has white spots on its back, with yellow centers in the spots -- just like eggs sunny side up, he says. Its babies live in trees, a meter or two or three above the forest floor.
An Italian colleague working the Amazon basin section of Venezuela might counter with the story of a tribe that reserves 2- to 4-foot-long earthworms as special food for expectant mothers or those who've just given birth.
But worms are more than novelties or foodstuffs. They are earth-movers and -shakers and -shapers.
As the late naturalist Stephen Jay Gould notes in "Hen's Teeth and Horses Toes," the "the very ground is being swept from beneath our feet; it is alive and constantly churning."
There's a riot of worms down there.