by Guy Murchie
Almost any of these motes of dust, particularly the ones that originated in soil or water, may include animal microbes that are dormant while dry or cold but awaken and start swimming when a cloud droplet happens to condense around them, perhaps eventually conveying them to Earth inside a raindrop. Indeed it is the clouds that are the most fertile parts of sky and every puff of cumulus or nimbus is unquestionably alive with tiny animals and plants that live there for generations (a microbe's generation often lasting less than an hour), eating, breathing, excreting, floating, swimming, competing, reproducing ... Most of them are less than one five-hundredth of an inch long and shaped in a hundred different ways, as the illustration (somewhat out of proportion) suggests, the larger ones ranging from algae, seeds and pollen to springtails and mites, often picked up by a cloud that slides up the windward slope of a mountain. The tinier ones, like bacteria and diatoms, may be lifted directly out of the sea by rolling fog, even bearing their own stores of phosphate, methane, carbon and sulfur dioxides and other nourishing compounds.
The fact that moisture in the air condenses only around solid nuclei of course makes dust a vital factor on Earth, without which there would be neither clouds nor rain nor fresh water nor life much beyond the sea. And the presence of many of Leeuwenhoek's creatures actually inhabiting the wind and rain reveals that life permeates the sky about as extensively if not as densely as it permeates all bodies of water and virtually all land.
MICROBE CLASSIFICATIONS
Something not generally realized about the microcosm even today is that it not only bustles faster than our visible macrocosm, but also, as more and more is revealed about it, it seems steadily to deepen in profundity until no distinction between animals and vegetables is left, for the good reason that the microcosm preceded both kingdoms in evolution and apparently remains Earth's prime proving ground for the basic inventions of life: growth, metabolism, sense, response, locomotion, reproduction, sex, death ...
The main divisions of the microbe world, in order of diminishing size, are first, the creatures of borderline visibility (mostly animals of the largest one-celled dimensions such as amebas, slipper-shaped ciliated paramecia, bird-beaked cladocerans, anteater-nosed thacheliuses, goose-bodied lionotuses, heart-shaped ostracods, wormlike nematodes, ova and the lamer plankton of sea and sky, averaging about 1/100 of an inch in diameter), second, the one-celled algae, fungi such as yeasts, small plankton, sperms and blood cells (ranging to about 1/5000 of an inch), third, such tiny plant life as bacteria, rickettsiae and primitive blue-green algae (averaging 1/25,000 of an inch) and finally viruses (around one 1/1,000,000 of an inch).
Such a vast complexity of animals, vegetables, animal-vegetables and possibly (in the case of viruses) animal-vegetable-minerals, does not make up a very neat hierarchy. Indeed no two biology books I have seen have classified microbes exactly alike - and how could they with nature herself apparently undecided as to how to rate her proliferation of primordial but constantly evolving miniature models? Yet, if for no other reason than that the total mass of microbes on Earth has recently been estimated to be a good 20 times greater than the mass of all earthly animals (including all animal microbes), we certainly cannot afford to neglect the microcosm.
Have you ever seen a paramecium? Although a single-celled protozoan discovered by old Leeuwenhoek in pond water, it is not what you would call really primitive like the simple and almost formless ameba for, in the course of its evolution (which has taken as many millenniums as our own), it has happened to develop an extraordinary complexity. Neither is it the biggest of protozoans, one unruly variety of which (called Chaos chaos) attains to a length of one fifth of an inch, but it is just visible and swims commonly in wet earth, often inside the stalks of green grass, and in dry weather it may sleep encysted in hay or dust almost anywhere. It is shaped like a slipper, but glides "heel" forward except when maneuvering around an obstacle, propelled by its thousands of cilia that row in eight or ten flashing waves of continuous coordinated stroking down its body (page 27), some of them at the same time whisking food into the funnel-shaped mouth, the while gyrating in a corkscrew course due to the oblique angles of the cilia and perhaps the skew of the oral groove that leads to the mouth. When it wants to back up, the creature instantly "shifts gear" and all its cilia paddle in reverse, and it can turn in any direction.
Like all living cells the paramecium has a nucleus to direct its growth, and the bubblelike vacuoles that enclose its digesting food can be seen under the microscope slowly circling around this floating center in the transparent body, the undigested residue eventually arriving at a fixed anal pore to be evacuated. The animal breathes oxygen by diffusion through its surface and, after using it for the combustion of food as do all animals, it exhales or excretes leftover carbon dioxide and nitrogenous wastes along with excess water, which served mainly as a vehicle for the food. It may be worth mentioning too that the paramecium uses two special blossom-shaped organs for getting rid of these fluids (the "petals" of which are canals converging on the central bladder), and it is believed to be a world's champion in elimination, having been known to void its entire body volume of liquid in half an hour: 10 times faster than an ameba and 1000 times faster than a man. Other features are its "defense" arsenal of "poisonous harpoons," which it can shower against an attacker, and the extraordinary fact that some of its species have been observed to diversify into eight sexes, a subject we may look forward to delving into in Chapter 5.
Another common ciliate is called didinium and is a kind of shrew of the watery microcosm, specializing in preying on paramecia. It looks like an oil can decorated with two belts of flickering cilia and a snout on top, with which it pokes about at high speed. When it meets a paramecium it jabs into the soft body and easily sucks it into itself. Even though the paramecium is usually bigger than the didinium, it doesn't faze this pirate, whose snout gapes open into a voracious mouth while his sides bulge to accommodate the meal, soon turning him into a pulsing ball several times his original size. One might suppose an entire paramecium at one sitting would satisfy the didinium for at least a week, but an hour to such a microscopic creature must be equivalent to 100 times as long to a man, for the average didinium has been observed to waste away toward starvation if he eats less than half a dozen paramecia a day!
An animal that feeds on a similar principle but in a more vegetal manner is the suctorian, who usually attaches himself to something solid, then extends his dozens of tentacles straight out from his rounded center, like an octopus with open arms. As soon as any softbodied victim blunders into a tentacle, even if it is 10 times bigger than he, it is grabbed in several places and sucked "dry" in about 15 minutes, while the suctorian balloons beyond recognition.
But to get down toward the essence of life we had better look closer at that simplest of all creatures that are indubitably animals: the ameba. This variable one-celled blob of protoplasm lives almost anywhere life exists, from the bottom of the ocean to the topmost crests of sandstorms swirling over the Sahara, including the inside of your body, and is sometimes visible to the naked eye as a white speck one fiftieth of an inch across. The most essential of its parts is the nucleus that drifts about inside the surrounding jelly (made of protein, sugar, starch, fat, etc.) called the cytoplasm. The latter is enclosed in an almost imperceptible membrane, without which the creature would quickly lose itself by diffusing outward. Yet the membrane lets water and gases flow through it easily, and, if the ameba is cut in two, both halves will immediately seal their unprotected surface with new membrane.
Being without a fixed form, the ameba takes naturally to "walking" on temporary "legs" and eating with a momentary "mouth," these appendages often serving both purposes at once. We have already described its strange oozing locomotion (page 26), which entails using nearly every iota of its cytoplasmic jelly as a leg at some stage of its gait. And, curiously enough, it eats with only a slight variation of the same oozing motion, in effect swallowing its prey through a
kind of outflanking maneuver of its leg-lips, like an army surrounding an unwary enemy. If this suggests that an ameba habitually puts its foot in its mouth, at least it is deft enough to create a throat with the same encircling gesture, and as the throat carries the prey inward it becomes in turn a "food vacuole" or wandering stomach of water that was swallowed with the meal and in which the struggling prey will soon be digested - that is, if it doesn't first break loose again, a common denouement among amebas, who can never be sure any mouthful is really "down" until it has been drugged into submission by digestive juices. Superfluous liquid of course is voided (as with the paramecium) from a bladder vacuole that periodically piddles it through the outer membrane.
Another branch of the microworld I should mention is a completely different phylum of animals, called rotifers because they seem to have rotating heads. Though smaller than paramecia and most other protozoans, they are vastly more complex for they are metazoans (multicellular), which means that their bodies contain not just one but hundreds of cells wonderfully specialized and combined into such organs as eyes, brain and developed muscle and nervous systems. And, like most other microbes, rotifers come in many varieties, including some that float on ponds as transparent bubbles, some that look like worms and some that live in graceful "ivory towers" built of their own molded fecal "cobbles." But the most familiar sort has the amusing form of very proper old ladies standing wrapped in furs and tight skirts with elaborate ciliated coiffures and, as Leeuwenhoek put it, "all aquivering and ashivering." Some of them look ridiculously like dowagers standing gossiping outside the opera house in a snowstorm while awaiting a taxi, balancing on their little feet, intermittently doubling up in fits of mirth or leaning toward each other all atwit over a juicy anecdote, and you can see in the microscope the orbits of the swirling "snowflakes" stirred by their gyrating heads. Reinforcing the illusion is our certain knowledge that these fluttery figures are actually females, for rotifer males are few and ironically much smaller than their "wives." Yet either sex can telescope by pulling feet and heads into their barrel-shaped mid-regions preparatory to encysting themselves against drought or danger, in which state they look like tired poodles beside their uncysted dowager companions. Their ability to seal themselves into their "barrels" while awaiting better times is obviously important in their evolutionary success, for they are extraordinarily cosmopolitan and travel constantly upon the feet of birds, on other animals and vehicles, including microscopic dust carried by the wind, which results in their being found on every continent, in every desert and ocean, even frolicking about in hot springs and sleeping upon glaciers in Antarctica. When not stowing away they can also travel either by walking like inchworms, using both ends for feet, by swimming individually with their cilia crowns serving as propellers, or swimming collectively, a dozen or more of them joined by their feet and radiating outward to form a revolving sphere. When feeding, however, they keep their regular feet firmly planted by gripping any solid object with glue supplied by special glands, while, at their head ends, everything they suck in and swallow passes through the "jaws" of a chewing mill with muscle-operated teeth that, in some species, resemble a row of bird beaks that can reach out to peck reluctant crumbs.
The roster of odd beings in the little world below our normal vision thus seems as endless as it is fantastic, and I imagine Leeuwenhoek could not have been more fascinated if he were discovering the fauna of Mars.
PLANKTON
Where the microcosm is most dramatic in scale, if not significance, is in the ocean, where plankton live everywhere in numbers far exceeding the stars of the Milky Way or even of all the billions of Milky Ways now known to exist beyond our own. The word "plankton" appropriately derives from the Greek for "wandering" (just as the related word "planet" came from "wandering" as applied to the "stars") and is now used to designate all the minute swimming and drifting life of the fluid seas. A good way to introduce oneself to the incredible quantity of planktonic beings might be first to try to visualize the 100-odd scattered specks of shrimplike, rounded or wormy animals in a cubic foot of average seawater as they swim about browsing on some 10,000 invisible crystalline plants among an estimated 100 million much smaller bacteria, algae and protozoan creatures, many of them inside the bodies of their larger companions. Although the most fertile plankton regions are a lot more populous, this probably is pretty accurate for a random bucketful of ocean, 147 billions of which are actually present in each one of the 340 million cubic miles of the earthly seas!
It is hard to decide what is the commonest kind of plankton animal because every phylum in the kingdom has at least some members living in the sea and very likely all of them are to be found somewhere among plankton, one certainly being the phylum of Chordata, which includes fish and man. Crustaceans, however, seem to be the most frequently mentioned class of plankton animal. I mean particularly the ubiquitous shrimplike copepods that range from the size of a rice grain down into invisibility and, under a magnifying glass, look iridescent, now blue, now green, now yellow, as they turn their humped little bodies, the while twiddling their legs or rowing jerkily along with feathery oars. Sometimes, they and their companions make one think of buffalo grazing restlessly on an ancient Wyoming prairie in spring - wee pirouetting bison amid a smattering of odd-shaped, prancing horses, elk, sheep, giraffes and kangaroos. The analogy is apt because they really are grazing, though on diatoms instead of daisies amid green algae instead of green grass. But copepods could hardly be more exotic, trailing graceful scarfs in pink, blue and purple, as they jostle among new-hatched finny fry with staring silvery eyes, here dodging a ghostly globe of fish eggs, there a slithering, bristle-nosed arrowworm or a pteropod "sea butterfly" that corkscrews upward, looking like a cross between a spaceship and a bumblebee.
Some plankton sprawl with multigesticulating tentacles like tiny octopuses, some throb as breathing lampshades with tasseled fringes or glow at night while flashing red, white and blue lights around the rims of their umbrellas. One kind, the polychaete worm, is as transparent as glass and swims with forward undulations while paddling his 30-odd double flippers, but, when frightened, rolls into a tight ball to plunge elusively down to a "safer" level of society. Now and again along will come a bustling baby barnacle, an infant mackerel or perhaps a two-inch shrimplike krill, favorite fare of whales and seemingly a whale himself beside the microscopic copepods and diatoms. Up, down and on every side one beholds a hundred animal fantasies through the lens in as many seconds of watching.
There is seemingly no end to the unfolding details revealed by increasing magnification. Even vegetable plankton such as diatoms, initially too small to see, appear in the magnifying glass as beautiful skeletons shaped like spheres or triangles or diamonds or boats, with hundreds of "holes" in them arranged in curious symmetric patterns and serving as geometric sieves that strain the teeming sea. But in a powerful optical microscope the "holes" themselves turn out to be hexagonal sieves full of much smaller "holes," which, through an electron microscope, are revealed as still smaller sieves made of even smaller "holes," the descending series continuing down to molecules in the form of crystal lattices composed of atoms that are made up of elementary particles that act and react as abstract waves of energy...
Such microvegetables dwell in the upper levels of the sea where sunlight penetrates and "cooks" their meals by photosynthesis, just as in grass and trees. Plankton animals, on the other hand, do not have to stay so high, for, although they climb to graze in the lush upper pastures (mostly at night), they can also browse below upon the spicy, if less green, bits of dead and decaying plankton that perpetually settle through the black depths, like a slow snowstorm laced with vitamins and spiked with phosphates, nitrates and iron compounds that are continually being washed off the land by millions of little streams before being transported down hundreds of big rivers to add their share to the oceans' salts. Some of the larger plankton animals can swim upward as fast as 500 feet per hour, and even the microscopic
ones will climb perhaps 25 feet in the same time for their nightly greenery. Some are thought to sleep during the winter in the cooler waters, a kind of microcosmic hibernation. A few manage to migrate vast distances in the bilge water of ships, thus significantly propagating their kind throughout the seven seas.
Some are barrel-shaped and eat, breathe and swim all with one continuous pulsating motion, sucking in water at the open head end, straining it, then expelling it out the open tail end on the ramjet principle. Some live in snail shells buoyed on bubbles. Some are bellshaped medusae with pendulant elephantine trunks that ingest tiny animals picked off their tentacles, the tentacles having first captured them with stinging cells called nematocysts. The nematocyst, by the way, is an extraordinary but widely used automatic weapon (found in various forms on the tentacles of all fresh- and saltwater polyps and jellyfish) that explodes when any animal touches its hair trigger, first scissoring a tiny gash in the skin of the victim, then instantly shooting a long microscopic syringe through the breach with such high hydraulic pressure that the jerk it undergoes at full extension bursts its tip, flooding the deep wound with a paralyzing poison!
Perhaps most amazing of all plankton animals, however, is a microscopic flagellate called Oikopleura, some species of which range down to the size and shape of a human sperm, who builds a "fish trap" (for catching bacteria-sized food) so elaborate and efficient that nothing in man's vast array of fishing gear can approach it. This contraption first appears as a kind of second skin secreted out of his own body pores, a clinging envelope around him that is both transparent and elastic. Then, having neatly pared himself from it with his long tail, he undulates the same tail to pump water into it, rapidly inflating it about him like a balloon, the while spinning thread inside it and weaving a set of webs beyond the capacity of any spider: two coarse grids across the double front doors to bar intruders above edible size, and two cone-shaped fine-mesh nets within to funnel food from the entering streams directly into his open mouth. The whole "machine" is thus a sophisticated, continuous and almost automatic trap, streamlined to facilitate its jet propulsion through the sea, as its pilot-owner with waving tail keeps its internal currents flowing and presumably a careful eye on its five hatches, one of which is an escape port under the bowsprit, just in case -
