Trow . — The Karyology of Saprolegnia. 629 
the points of difference between us are trifling, and concern 
the behaviour of the nuclear wall, which Hartog considers 
to remain intact, and the position of the half-rods back to 
back, and not face to face, as I have found them. As he 
expressly states that divisions do not occur in the oogonia, 
I conclude that he observed these phenomena in the antheridia, 
where they certainly occur regularly. 
It is clear then that by the time typical vacuolization 
has begun, a reducing division of the nuclei, and the dege- 
neration of the large majority of the daughter-nuclei thus 
formed, have taken place in the oogonium. The fact that it 
is the smaller half-chromosome that generally undergoes 
degeneration, and that the nuclei are slightly larger on the 
average at a later stage, leads me to believe that it is the 
smaller nuclei that go to the wall in this struggle for the 
survival of the fittest. 
But an oogonium of 50 ju, diameter does not produce forty-five 
oospheres, and as the oospheres are uninucleate, it is clear that 
we have to explain how the number of nuclei is still further 
reduced. The vacuolated stage of the oogonium passes away 
and is replaced by one in which we have a thin layer of proto- 
plasm lining the wall and surrounding the vacuole. Fig. 12 a 
and b represent two out of six sections, 7-5 fi thick, of an 
oogonium whose greatest diameter measured about 45 /z. The 
nuclei which could clearly be distinguished by any definite 
recognition marks numbered forty-one. Of these seven were 
noted as typical and thirty-four as degenerate. Three typical 
ones are shown in Fig. 12 b and twelve degenerate ones in 
Fig. 12 a: an oogonium of this size would produce about 
seven oospheres. The typical nuclei have the structure already 
described. The chromosome is small and its spongy character 
cannot be determined, simply because in order to see the 
nucleus at all it is necessary to stain as deeply as possible. 
The degenerate nuclei present various appearances : some of 
them stain so badly that they are not readily visible, and can 
be identified only by careful comparison with more deeply 
stained ones. The deeply stained nuclei have the appearance 
