Freshwater volvox colony. Inside you can see zygotes that will survive in winter time. In favorable conditions volvox reproduces asexually and new colonies are formed inside and then leave the "parent." You might notice that zygotes are concentrated only in one half of the colony. That's the posterior (rear) end, which means when the colony swims, the zygotes stay in the back.
volvoxalgaepolarized lightmicroscopeblack background