3B2 WILLIsTON: DiIscoID GEMMAE IN RADULA 
to the median wall before the apical cell becomes established, 
In case the two apical cells of a single gemma behave differently, 
there is an asymmetrical development of the gemma. If one 
apical cell becomes established before the other, it usually but not 
always ceases to function before the other; so that it is common to 
find a gemma with one apical cell cutting off a segment in the 
normal way while the other has already divided by a periclinal 
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BY 
12 18 1h 
FIGURES 5~14, Radula flaccida. Gemmae in various stages of seers 
from single cell Stage to the mature form. 5—7 show the gelatinous substance ger 
early divisions, X400. 8~—12 show th pical cells a, X 400. 14, mature Co 
funnellike elevation and basal cells, X66. 
wall (Fic. 17). The same condition was observed in F: . 
blanata by Stevens (10, p. 370). This irregularity in the man . 
of establishment of the apical cell makes it possible to phi 
three types of gemmae: those in which the original apical ee 
rants begin immediately to function as apical cells (FIG. 9 a i 
those in which the apical quadrants cut off cells parallel wit 
