First discovered in 1700 by Antonie van Leeuwenhoek, the microscopic spheres in this video are Volvox, a genus of chlorophyte green algae. If you enjoy this video, its creator Shigeru Gougi posts absolutely astounding microscopy images on his Flickr stream. Want to explore the Volvox realm yourself? From Microbehunter Microscopy:
Microscopists who are interested in observing Volvox should try to investigate water samples from ponds and puddles. It is also possible to grow Volvox at home. Volvox likes to grow in nutrient-rich water. Dilute some plant fertilizer in water and add some pond water containing Volvox (or other green algae that you want to grow). Place the container on the window sill for several days but prevent direct sunlight as this may cause overheating, and drives out the CO2 for photosynthesis from the water. Alternatively, you can also use a plankton net to catch the colonies.
Learn more at The Kid Should See This.