On Two New Members of the Volvocacese. 133 
(Fig. 14, B), the pyrenoid increasing simultaneously with the growth 
of the cell. The pyrenoid shows signs of elongation transverse to 
the cell-axis (Fig. 14, A) and eventually it divides into two equal 
portions (Fig. 2 B). At the same time the chloroplast begins to 
split, starting at the posterior end, the line of division running 
Fig. 14. Pyramimonas delicatulus. A, Pyrenoid elongating; B, Pyrenoid 
divided; C, Chloroplast dividing; D, Nucleus divided; E, Form with five 
cilia ; F, Cell-membrane invaginating; G, Form with eight cilia ; H, One of 
the two individuals produced on the completion of fission ; I-J, Posterior axial 
view; K-M, Dividing individual (x 800). 
through the small flask-shaped cavity. The cell-membrane, 1 up to 
this stage, has not shown any sign of division ; it is merely the 
chloroplast that is dividing. The line of division passes through 
the thick posterior portion of the chloroplast, between the halves of 
1 Like other members of the Polyblepharidecs, Pyramimonas does not 
possess a cell-wall of secreted cellulose. The protoplasm of 
the cell in contact with the surrounding water, is of a firmer 
consistency than the inner portion. The outer differentiated 
layer is protoplasmic and therefore differs essentially from 
the secreted cell-wall of Chlamydomonas. In this sense, 
therefore, Pyramimonas cannot be said to possess a cell-wall. 
Hence “ cell-membrane ” is used in preference to the less 
correct term. 
