370 STEVENS: DIscoiD GEMMAE IN LEAFY HEPATICS 
portion of the gemma, which may be regarded asa poorly defined 
stalk. 
The two cells formed by the division of the outer cell behave 
as more or less independent portions. They divide without very 
definite order by transverse and longitudinal walls (FIG. 2, C) 
and soon a wedge-shaped cell is cut off in one (FIG. 2, D) or both 
(FIG. 2, E) of the portions. These cells function for a while as 
two-sided apical cells. The irregular occurrence and behavior 
E 
FiGuRE 2. Radulacomplanata. A-C. Gemmae in early stages of development, 
300. D. Gemma that has formed one apical cell, X 300. HL. Gemma with two 
apical cells, X 300. Dotted line indicates gelatinous secretion. 
of these apical cells gives rise to the considerable variation in form 
which is to be observed in the gemmae of Radula complanata. 
For both portions may cut off apical cells at the same time and 
develop with equal rapidity, thus forming a symmetrical gemma, 
or one segment only may form an apical cell, in which case the 
segment which has no apical cell will develop very little and will 
be more or less crowded out of position. Such a gemma is shown 
in FIG. 3, A. One portion has here developed an apical cell which 
has cut off six segments. This portion has increased by further 
cell divisions until it is composed of twenty-three cells, while the 
portion having no apical cell is composed of but four cells. 
Moreover, the apical cells do not persist until the gemma is 
mature; but, after cutting off segments in regular succession for a 
time, lose their capacity of regular segmentation and divide by a 
periclinal wall (FIG. 3, Band C). After this first periclinal div- 
ision the apical cell divides like other cells by longitudinal and 
