Trow . — The Karyology of Saprolegnia. 635 
of the nucleus, too, at this stage, presented some difficulty, as 
it was distinctly unlike that of the oosphere-nucleus. A careful 
search was consequently made for stages intermediate between 
these two which would account for the change in the nuclei. 
These were soon found, and it was noticed that the nucleus 
of the oosphere gradually became larger and more irregular : 
indeed, the appearances led me at first to suppose that the 
chromosome-mass divided up into small portions which laid 
themselves in contact with the nuclear wall. Though I now 
believe this view to be incorrect, it will be seen from Fig. 17 
that it was more or less reasonable. As a matter of fact, in 
consequence of the study of the dividing nuclei of the oogonium 
and a later examination of the oospore-nuclei in 5 . Thureti , 
I have come to the conclusion that the small gameto-nuclei 
undergo changes in virtue of which the microsomata in 
proximity to them become deeply stained ; the chromosome- 
mass becomes of smaller and the nucleo-hyaloplasm of larger 
volume. As the small chromosome is more or less masked 
by the large microsomata, it is difficult to detect it in carmine- 
preparations at this stage. These changes in the nucleus 
agree in most respects with those which precede its division 
in the oogonium. 
During the course of this investigation of the nuclei, oogonia 
in the condition represented in Fig. 18 were several times 
observed. I think they place beyond all doubt the occurrence 
of fertilization in 5 . dioica. The nuclei of the fertilization- 
tubes and oospheres are at this stage of identical structure. 
A nucleus is frequently seen at that point of the fertilization- 
tube which is in contact with the naked oosphere. Occasion- 
ally one observes, as in the figure, a second nucleus in the 
oosphere lying at its extreme edge, and in such cases one 
always finds by careful examination that a delicate cell-wall 
has been formed around the oosphere, and that there is a 
fertilization-tube exactly opposite to this lateral nucleus. No 
opening can be seen in the tube, and it would in any case be 
probably very difficult to prove its presence even were it 
there. But a permanent opening does not appear to be 
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