88 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
the formation of a specialized layer of protoplasm, perhaps of the 
same nature and formed in the same way as the hyaline zones 
observed by Harper (’ 99 ) in Pilobolus. This layer begins just out¬ 
side the centrosome and is formed progressively from that point 
until it encloses the plasma of the future spore. In figure 24 (pi. 8) 
it is not yet half completed. It is very thin at first, but gradually 
thickens and since it stains differently from the rest of the proto¬ 
plasm, is quite clearly definable. That this limiting layer of proto¬ 
plasm is a membrane, however, is very doubtful, and that it is 
composed of fused astral rays is contrary to my observations. 
That the astral rays do not fuse is readily demonstrable in 
Hydnobolites. They are very long during the spindle stage, and 
do not materially alter in length after that. They do change their 
position, it is true, but the change is one that throws them farther 
apart instead of bringing them closer together. Fusion is, there¬ 
fore, a physical impossibility. The only way in which fusion could 
be effected would be by the flattening of the rays, or by a growth 
of lateral wings on each. But a polar view at this or any other 
stage presents no such transformations. The rays are distinct and 
unchanged, and the limiting layer is of uniform thickness. Indeed, 
it is quite obvious that whatever the composition of the limiting 
layer may be, it does not consist of fused astral rays. 
While the spore plasma is being separated in this way, it is 
observable that a change is taking place in its structure. Starting 
from the nucleus the protoplasm that is to be included within the 
spore becomes more finely reticulated and eventually more hyaline 
than that outside. Such a change suggests that there may be a 
connection between the refining or differentiation of the spore 
plasm and the formation of the limiting layer. 
About the time the limiting layer is being constructed, the nuclear 
wall is formed. When the completed nucleus is first demonstrable, 
it presents the appearance of a short cylindrical vesicle. It then 
elongates, growing towards the center of the spore mass, or to one 
side or the other at any angle (pi. 8, figs. 26, 27). Meanwhile it 
retains its cylindrical shape. Eventually it grows beyond the mid¬ 
dle of the spore, so that its length may be equal to three quarters 
the diameter of the spore. Likewise it becomes bottle- or flask¬ 
shaped, the neck becoming quite tenuous (pi. 8, figs. 29, 82). But 
this “ beaked ” shape is not evident until long after the spore is 
delimited. 
