1906] YAMANOUCHI—POLYSIPHONIA VIOLACEA 409 
the cell (figs. 35, 42), a large vacuole being present in the center. The 
mechanism of constriction by the cleavage furrow is probably greatly 
assisted by the presence of this single vacuole, in place of numbers 
of smaller ones which are found in the tetraspores and carpospores. 
SPERMATOGENESIS. 
The sperms or spermatia are formed normally on special short 
branches called antheridia, which are developed in clusters at the 
tips of the main filaments. The 
antheridium consists of an axial 
siphon (diagram 1) which becomes 
surrounded and covered by a large 
number of small cells. These 
generally develop sperm mother 
cells at the periphery of the anthe- 
tidium, and may consequently be 
called “stalk cells.’ The mitoses 
in the axial siphon of the anthe- 
tidium were studied (fig. 52), as 
well as those which form the stalk 
cells (fig. 53), and they showed 
the number of chromosomes to be 
20. The methods of chromosome 
formation, the development of the 
Mtranuclear spindle, and the cell 
division by constriction are the 
Same as those of the vegetative cells 
already described. 
h . DIAGRAM 1.—Section of an anthe- 
€ formation of the Sperm jidium, showing position of axial 
mother cells from the stalk cells _ siphon, stalk cell (sc), sperm mother 
(fig. 54) is illustrated in jigs. 55-61. cell (sme), and development of the 
‘8. 55 presents the prophase of “P°™ 28 
of the mitosis, fig. 56 metaphase, fig. 57 the equatorial plate viewed 
from a pole, fig. 58 shows anaphase, and jigs. 59 and 6o illustrate 
telophase. The cell division by constriction is shown in jig. 61: 
he Sperm mother cell (fig. 62) increases in size and assumes its 
characteristic form, which is narrow at the periphery and swollen at 
the base. In rare cases the formation of the stalk cell is omitted, 
