"HOW SOME JELLYFISH ARE BORN" "Outside the marine biology station at Roscoff, Ìn Finistere lies a channel of water where many types of animals live." "At low tide it's easy to collect whatever's sheltered in the rich forest of algae, hiding in the roots, attached to the stems or crawling along the surface." "We choose a clump of algae." "That's the common habitat of the animals we wish to study." "We place a branch of it bearÌng the desired animals into an aquarium." "We have to move in very close because these animals are very small." "These polyps resembling mÌnuscule amphorae are actually only 1 or 2 mm long." "Essentially a stomach attached to the algae by a foot, the animal is surrounded by three rings of tentacles." "The floating limb bearing the mouth extends effortlessly." "Each tentacle ends in a bud composed of hundreds of poisonous cells, making it look like a blackberry." "These cells burst at the slightest impact, projecting a filament 1/20 mm long that harpoons its microscopic prey and injects it with a paralyzing poison." "The animal explores the surrounding water with its flexible neck and tentacles." "Once the prey is paralyzed, it must be inserted into the mouth headfirst." "The animal reproduces by budding." "The buds deform its rear section." "Several days pass before the buds hatch but thanks to film we can look at it speeded up." "With the naked eye, no movement or transformation Ìs discernible." "But speeding it up 400 times, we observe in just seconds the little polyp's final stage of development and see it break out of its casing." "The newborn floats freely for several days and then attaches itself to algae." "Among these algae one can also find rather remarkable crawling jellyfish." "Their discs measure I/2 mm in diameter and have 6-12 tentacles." "Each tentacle forks into two branches." "One branch ends in a sticky pad that allows it to move about, the other ends in a sac of poisonous cells that capture prey." "Once the prey is paralyzed, it must be eaten." "That's no easy task." "The jellyfish is able to push out its stomach." "In any case, the prey must be introduced- this time rear-first- into the jellyfish's mouth, which readily dilates." "Reproduction takes place via buds formed inside the jellyfish." "They later emerge and become a miniature replica of their parent." "The buds develop slowly, and the parent's movements are equally slow, but speeded up 200 times, the strenuous efforts of parent and bud to separate become clear," "Let's return to normal speed." "After a few days, the bud can secure its own food." "When the cord of living matter linking it to its parent becomes sufficiently thin." "The offspring detaches itself from its parent." "Reproduction can also occur via the eggs we see inside the jellyfÌsh." "In some that are both male and female self-fertilization occurs." "Each egg produces a larva 0.1 mm long that swims by means of vibrating cilia." "It will turn into a polyp, fix itself to one spot, and eventually become a crawling jellyfish." "This larva resembles the previous one, but it will bud into hundreds of polyps and form a colony." "Such marine colonies are found in this estuary, flooded by the rising tide, and spanned by a railway bridge 1,25 miles from its mouth." "At low tide, the sea takes with it everything on the freshwater riverbed." "At very low tide, the bridge's central pillar stands on dry land." "We easily collect well-populated branches from around its base." "This time it's not algae that we put in a sea-water aquarium, but animals sharing a common substance and a common structure." "Together they can reach a height of eight inches." "Using a slight magnification, we see that the colony puts forth filaments to grow within which we can trace the path of digestive particles with a microscope." "A succession of contractions dilations and stand stills enables this circulation throughout the colony by periodically reversing direction." "By speeding up the film up to 1,000x, we see the 1/5-mm-wide filament growing." "We can also see the contractile plumes of the polyps that feed the colony." "Plumes loaded with poisonous cells." "Under the microscope, speeded up 800x, over the course of 72 hours we see one of these stomachs forming." "The filament grows in both smooth and ringed sections." "It narrows four times and then expands significantly to create a feeding organ." "When it reaches 3/4 mm long, the casing stops growing." "The stomach can now be discerned surrounded by separate tentacles." "Due to the movement of the polyp and perhaps a chemical change, the top of the casing is finally cut away around its circumference and opens like a lid, allowing the plumes full of venomous cells to open out." "Let's return to the colony, lt reproduces by means of jellyfish formed in sealed tubes 1 mm long." "The jellyfish emerge at a set time - here, 11 a,m, and 8 p,m." "It is noon, and we will see the evening hatching." "The jellyfish are like a flight of butterflies 1 mm in size." "It takes a speeded-up camera and a microscope to observe their formation." "We're witnessing the final stage of the phenomenon, when the jellyfish are ready to come out." "They grow very slowly but come out very quÌckly, so the camera speed must be changed at just the right moment." "At each hatching, two jellyfish emerge with a half hour between them speeded up here to a few seconds." "These jellyfish retain the contractility and the venomous cells of their group." "They are male or female depending on their colony, and they'll release their reproductive elements into the sea where fertilization will take place." "From this, larvae will develop as we saw earlier giving rise to new colonies."