170 
W. B. Grove. 
Figs. 1-11. Pleodorina illinoiensis (except Fig. 6). 
Fig. 1. Mature coenobium, x 360. 
Fig. 2. Mature 16 celled coenobium, x 360. 
Fig. 3. A mamillated posterior end, x 360. 
Fig. 5. Mature antheridial colony ; the gelatine is much softened and the 
antherozoid-plaques are ready to escape. The four anterior cells are undivided 
(only four antheridia are filled in, the remaining 24 are similar) x 180. 
FiG. 5. A coenobium, viewed from the anterior end ; the arrows show the 
direction of rotation. (Somewhat diagrammatic). 
Fig. 6. Pleodorina californica, from a mounted specimen (California), x 180. 
Fig. 7. A 32-celled plakea seen in plan. The four unmarked cells in the 
centre will be the anterior cells of the phialea ; the unmarked ones at the 
