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The brown spherical objects (1)are the sporesof Didymium that have germinated. Each spore produces a single amoeba.     Each amoeba has a contractile vacuole(2)and a single 'fried egg' nucleus (3) and they move, feed, and divide like free living amoebae.   Eventually two compatible amoebae  fuse and the nuclei also fuse to give a diploid (2n) nucleus.  This diploid nucleus then divides many times synchronously to form a multinucleate (millions of nuclei) plasmodium like you see here (click).