Painlevé’s first film on animal behavior, focusing on the Hermit Crab. On this film we see the Hermit Crab trying to find shelter.

Underwater photography, magnified close-ups, and film through microscope present the sea urchin, a complex creature. We see their mouth and five teeth close and open. After injecting one with gelatin, the shell is removed and we see the muscle structure, digestive tube, and reproductive organs. Magnified stems reveal suction cups; stems lengthen and contract allowing the sea urchin to move. We see microscopic calcareous stems; at their ends are jaws with various uses. Cilia everywhere are in constant motion, stirring up water and debris. African music on the soundtrack suggests a shuffle dance.

At a marine biology station, a clump of algae reveals polyps, stomachs with limbs, limbs with buds, buds with poison cells. This animal reproduces by buds, which we watch close up in time-lapse images. In another kind of jellyfish, the buds grow inside then live outside for a few days until being on their own. Another produces eggs, sometimes self-fertilized. Some single eggs become buds with colonies. Another clump gathered at low tide consists of filaments of a colony - plumes with poison ends. In images taking 72 hours, we see filaments grow and produce a feeding organ from which a plume emerges. New jellyfish emerge from buds twice a day at set times to form a new colonies.

After a comic introduction, we look closely at a shrimp. Eyes on stilts, color patterns, pinchered walking feet, a rostrum. We watch shrimp eat using a strong claw and a fine one; we watch digestion. After eating, shrimp clean themselves. The female lays eggs that cling to her feet. After three weeks, the eggs hatch explosively. Few larvae live to adulthood. We watch an adult shed its carapace with a final leap, leaving it vulnerable; other shrimp attack.

In a freshwater pond, it's "eat or be eaten." A dragonfly larva eats a midge; a water beetle larva eats a damselfly larva. Snail larvae grow. A beetle larva eats one. Up close, we see the eating apparatus of a damselfly larva—with a retractable hook beneath mandibles. Some creatures bite and chew, others suck. A water beetle larva holds on to its prey, injects a poison that turns the victim's insides to soup, and then sucks it dry. We watch one eat a damselfly larvae and then another water beetle larva. Some have ingenious ways to camouflage themselves, like the water scorpion, and to breathe air while hunting under water. Caddisfly larvae hide in debris, then eat.

The one-celled long and slender diatom, up close: discovered in 1703 with the invention of the microscope. We observe them magnified 10,000 times: water expelled through the skeleton, mucilage constantly emitted, allowing it to glide. Their energy comes from sunlight. They divide and disperse. The narrator, conversing with a young woman, says their remains cover one-third of the earth's surface. They have uses in petroleum, explosives, and polish. Some live in isolation, some in colonies, like elaborate fans. They can move in clusters. Many small animals eat them. We watch them slide on each other in long strings.

A close-up look at sand urchins and rock urchins. At the seashore, a man digs up a sand urchin. We look closely. He sets it back in the sand, and it burrows out of sight. Its intestines take nutrients out of sand. Using magnification 200,000 times normal size, we see a rock urchin's spines with suckers on the end; a drawing illustrates how they work. A sea urchin walks toward a rock. We see three-fingered jaws—pedicellaria at the end of flexible stems—take in algae and other bits. We also see cilia less than 0.001 ml in length; their motion constant, creating whirlpools. On the shore again, we watch the setting sun. Occasional titles in French tell us what to watch for.

Titles in French and English help us know what we're seeing. In all waters, daphnia abound. They are crustaceans about 2 ml long, with one eye that turns in all directions. Antennae enable daphnia to move: in a close up magnified 150,000 times, we see the muscles of the antennae pulse. We see the eye, the nerve mass, blood globules, and the heart, beating several times per second. The intestine forms a long line. All are females; eggs develop above the intestine. New generations come rapidly. Inside each daphnia are tiny infusoria; we watch them clean the intestine of a dead daphnia. An enemy, the hydra, approaches. A daphnia dies, but many remain.

An educational film, a movie through a microscope, in two parts. Within minutes after the egg drops in the water, fertilization occurs and contractions start. Soon, in a fertilized egg, we see the germinal disc divide into two blastomeres. Divisions continue; contractions re-occur at the cap as it covers the egg. Title cards in French tell us what to watch for. Muscular movements and circulation appear; the heart beats. In part two, we see blood circulation begin as red cells develop on the surface of the yoke. They mass toward the heart. Arteries form, blood flows. The egg hatches and blood flows to new areas.

The film begins with methodical descriptions of one-dimensional, two-dimensional, and three-dimensional space. It then looks at a two-dimensional world inhabited by flat mice. It imagines how a human, from the third dimension could interact with that world. It then suggests how beings from a fourth dimension might interact with us. Next the film posits time as a fourth dimension, with scenes to aid comprehension. An off-screen narrator, graphs, and clever photography provide explanations and illustrations. The film asks viewers to use their imaginations.

Jean Painlevé short film examining population explosion and decline.