Arguments are presented for the symbiotic acquisition of microtubule systems prior to the acquisition of mitochondria in the evolution of eukaryotic cells. These arguments are based on distribution of organellar systems (microtubules more widely distributed than mitochondria, mitochondria more widely distributed than plastids) and on polyphyly (multiple origins of mitochondria, plastids, motility symbionts, extracellular bacteria and other xenosomes are easily demonstrable). All mitotic and meiotic eukaryotes are purported to have evolved from associations of Thermoplasma-like archaeobacteria with Spirochaeta-like symbiotrophs. The former bacteria are thought to have been ancestral to the protonucleocytoplasm whereas the latter supplied eukaryotes with their microtubule-based internal motility systems.