asporangium. The gametophyte fills almost the entire 
spore, and all of the nuclei near the apex are enclosed in 
cell walls. Most of the nuclei show nucleoli and nuclear 
contents in varying degrees of preservation. 
Comparison with the existing Selaginella. 
Lyon (12) has fully described the development of the 
gametophytes of Selaginella rupestris and Selaginella 
apus. According to Miss Lyon the initial steps in the 
development of the female gametophyte are the rapid 
expansion of the protoplasmic vesicle and the repeated 
division of the nucleus. A thick envelope surrounds the 
vesicle, but this envelope becomes proportionately thin 
as the surface of the vesicle increases. ‘There soon devel- 
ops a large vacuole. 
At this stage (Lyons, Plate VI, figure 46) the female 
gametophyte consists of the exospore, the mesospore, 
the endospore, the protoplasmic vesicle—which now con- 
sists of a thin layer of protoplasm in which there are im- 
bedded numerous flattened ovate nuclei—and the vacu- 
ole. After the spore membranes have completed their 
growth, the nuclei undergo their final division—these 
divisions being marked by the formation of cell-plates 
and walls. 
In the living species of Selaginella the megaspore 
usually germinates in situ. The nucleus undergoes re- 
peated divisions, first producing a number of free nuclei 
that are subsequently surrounded by cell walls. This de- 
velopment occurs at the apical or scar end of the spore, 
and at the opposite end there forms a large vacuole. The 
multicellular female gametophyte is completely enclosed 
within the megaspore wall. As the gametophyte contin- 
ues to enlarge, the spore is gradually forced open at 
the tetrad-scar and the gametophytic body protrudes to 
some extent. Following, or simultaneously with, this 
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