352 Harper.—Sextial Reproduction in Pyronema 
fusion of protoplasmic substances for purposes of reproduction 
being that between the antheridium and oogonium. 
The passage of the antheridial nuclei through the tube 
into the oogonium, when once the way is open, is a rapid 
one. As has been seen already the tube is filled with anther¬ 
idial nuclei before its basal wall is dissolved. The opening 
formed is larger than that between antheridium and tube, 
the entire basal wall of the tube being disintegrated. As 
a result there is an actual protoplasmic continuity between 
the male protoplasm in the tube and the egg-protoplasm. 
The two masses fuse at their point of contact after the tube 
wall has disappeared, so that the male nuclei enter the 
oogonium not like so many independent sperms, each piercing 
the plasma-membrane of the egg, but by simply migrating 
from the one cell-body to the other through a continuous 
mass of protoplasm. The entire structure, antheridium, tube, 
and oogonium, have in reality become for a time a single 
cell bounded by a single continuous plasma-membrane. 
In passing into the oogonium, the male nuclei leave behind 
the bulk at least of the cytoplasm with which they have been 
associated. The cytoplasm of the antheridium has been carried 
to some extent into the conjugating tube, but for the most 
part it remains in the antheridium. The nuclei here, as in 
so many other cases, indicate their superior significance in 
sexual reproduction by leaving behind the cytoplasm which 
has hitherto been associated with them. 
One conspicuous result of this non-participation of the 
cytoplasm in the act of fertilization is, that the antheridium 
and conjugating tube remain turgid and to the superficial 
view unchanged for a long period after the fusion has taken 
place. Tulasne observed this and remarks, as referred to 
above, that if the macrocyst and paracyst do influence each 
other mutually, this at least produces no notable change 
in their external appearance. As seen in sections the anthe¬ 
ridium contains a series of large vacuoles in its central portion 
which were not present immediately before the migration 
of its nuclei (Figs. 15, 17, 20, and 21). The presence of these 
