1922] DUPLER—REBOULIA 151 
most likely to show the oblique inclination of the wall and the con- 
sequent triangular apical cell, although one would not necessarily 
err even in the interpretation of an oblique section. It seems to 
the writer that there is no room for doubt as to the. presence and 
functioning of a triangular apical cell (figs. 34-39, 41, 45). It 
is not probable that this cell functions as an apical cell more 
than a very few times, being soon “lost” in the growing embryo, 
where the apical function becomes distributed to a number of cells 
(figs. 40, 46). 
BASAL CELL.—The basal cell of the row of four also does not per- 
form uniformly in all cases. It may divide by a vertical wall into 
two approximately equal cells (fig. 36), or it may divide by an oblique 
wall (fig. 35). Wooppurn found “basal cells of triangular shape” 
to occur, probably arising as a result of oblique wall formation in the 
basal cell. Haupt found no case of this, and in the writer’s prep- 
arations it is not common. Should the first wall of the divided egg 
be an oblique one, it might be probable that the hypobasal would 
divide obliquely, resulting in a triangular cell at the base. While 
no mitosis was found as a direct proof, the appearance of a number 
of embryos (figs. 16-18, 30-32, 34) suggests that the basal cell may 
divide transversely instead of vertically, the basal of the two cells 
thus formed behaving as here described for the basal cell itself, 
while the other cell sooner or later becomes divided by vertical walls 
in the same way as its neighboring segment (figs. 28, 29). Vertical 
wall formation in this cell would probably be delayed for a time and 
the cell remain undivided, even after vertical walls have formed in 
the segments anterior to it (figs. 34, 36). It seems to the writer that 
very frequently the basal cell of the row of four undergoes no further 
division whatever, but very early becomes differentiated as a large 
conspicuous foot cell at the base of the embryo, retaining its hemi- 
spherical shape, very early showing denser contents than the other 
cells of the embryo, and becoming coated on its free margin by a 
heavy thickening (figs. 45-47). This cell often remains quite dis- 
tinct, even in late embryos, and may clearly be recognized both in 
sections (fig. 47) and in surface views of dissected embryos. Should 
the basal cell have divided transversely (as already suggested) the 
basal of the two cells formed may remain undivided. WoopBuRN 
