Mar., 1923] 
SHOWALTER — RICCARDIA PINGUIS 
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not to the right and left, but below and above. These divisions are best 
represented by a diagram showing the apical cell, the primary segment, 
and the cells into which the primary segment is divided (text fig. 2). In 
this diagram the plane 1-1 • • 1 represents the division which cuts off the 
Text Fig. 2. Diagram of the apical cell (a), and of the cells into which the primary- 
segment divides; explanation in text. 
primary segment from the apical cell a. The first division (2-2 • • 2) of the 
primary segment cuts off a ventral cell c (see also figs. 9, 13, 2, 4, PL XVI). 
The next division (3-3 • • 3) cuts off a dorsal cell d, and intersects the pre¬ 
ceding division wall (see also figs. 2, 4, PI. XVI). The third division 
(4-4 • • 4) is vertical, at right angles to the former two, and divides the mid¬ 
dle cell into right and left halves, e and e' (cf. fig. 4, PI. XVI). Apparently 
one of these last two cells may continue to divide as an apical cell, giving 
off right and left segments and becoming the axis of a new branch; or both 
cells e and e r may function as ordinary surface cells. I have not followed 
these later divisions critically, but all my observations are in perfect agree¬ 
ment with those of Leitgeb. Figure 9 shows a vertical longitudinal section 
of the primary segment ( b ) in process of its first division. This figure was 
drawn from the serial section adjacent to and preceding the one shown in 
figure 10. Figure 13 shows the secondary segments ( b r and c) in an arche- 
gonial branch, and was drawn from the serial section adjacent to and follow¬ 
ing the section shown in figure 12. Figure 2, drawn from the section 
adjacent to and following the one shown in figure 3, shows the secondary 
segments ( b’ and c ) in preparation for the next succeeding division. 
Miss Clapp reports that “the primary segment is divided by a vertical 
transverse wall into an inner posterior cell and an outer anterior marginal 
one.” I have observed this first division of the primary segment in a half 
dozen or more clear cases. All of these show this division wall in a diagonal 
plane intermediate between the horizontal plane and the -vertical transverse 
