A. Two Chlamydomonas cells. Scale bar is 10 μM. B. Vegetative Volvox spheroid. C. Sexual female Volvox spheroid. D. Sexual Male Volvox spheroid. Scale bar is 50 μM for panels B–D. E. Schematic of Chlamydomonas life cycle. Left side depicts the vegetative reproductive cycle of growth, and division by multiple fission. Right side depicts mating, diploid MT+/MT− zygotic spore formation, meiosis and hatching to produce four haploid progeny. F. Schematic of the Volvox life cycle. Left side depicts key stages in the vegetative reproductive cycle. Starting in the upper right are a mature spheroid, cleavage stage embryo, pre-inversion embryo, inverted juvenile, expanding juvenile, and hatching stage. Right side depicts the sexual cycle. Pre-cleavage gonidia from males and females undergo modified development to produce sperm packet bearing male spheroids and egg bearing female spheroids. Sperm travel as a packet, attach to a female, dissociate, enter, and fertilize eggs to form a diploid MTF/MTM zygotic spore. Meiosis and germination produce a single haploid vegetative progeny (either male or female) and three polar bodies.