Subset of volvocine species showing an increase in complexity, cell number, volume of extracellular matrix, division of labor between somatic and reproductive cells, and proportion of somatic cells. A: Chlamydomonas reinhardtii; B: Gonium pectorale; C: Eudorina elegans; D: Pleodorina californica; E: Volvox carteri; F: Volvox aureus. Where two cell types are present (D, E and F), the smaller cells are the somatic cells, whereas the larger cells are the reproductive cells (gonidia).