VOLVOCINA 53 



reproduction are known 2iS parthenogonidia : the plates of young zooids 

 which arise by their radial fission, curving into spheres to form the 

 new colonies, bulge into the hollow of the parent colony, where they 



Fig. 44. Volvox aureus. After Klein, a (x 180), A medium-sized colony 

 showing as round black dots the numerous "somatic cells" of which it is 

 made up ; the protoplasmic connections between them, and the cell-walls, can 

 only be made visible by staining. The colony contains three types of repro- 

 ductive units: daughter colonies (d.c.) produced asexually by division of a 

 single zooid ; ripe macro gametes or young zygotes (z) ; and young " antheridia " 

 {an) whose contents are dividing up and will eventually form microgametes. 



b, A colony of microgametes which has just escaped from the antheridium. 



c, Mature antheridia as seen in surface view of a colony ; in two the micro- 

 gametes are seen sideways and in two, endways. 



remain for a time before they are set free. The clusters (antheridia) of 

 microgametes arise in the same way. In some species the micro- 



