1904] DAVIS—OOGEN ESIS IN VAUCHERIA 87 
growth and activity, and as such is a dynamic center. There is a 
very close resemblance to certain of the Peronosporales (e. g., Pythium) 
whose oogonia have merely an accumulation of dense protoplasm 
in place of the usual well-defined coenocentrum. 
The growth of the surviving functional gamete nucleus presents 
some interesting features. ‘There is a marked increase in the amount 
of chromatin which fills the interior with numerous small granules 
on a very delicate linin network. The nucleolus does not increase in 
size, so that it appears relatively much smaller in the older nucleus 
than in the younger (compare fig. 11 with figs. 3 and 4). Fig. 11 
is of an oogonium almost at maturity, and jig. 12 is after fertilization 
and shows two gamete nuclei fusing and also the remains of three 
sperms which were unable to enter the egg. 
The final steps in the maturation of the egg, as has been frequently 
described, consist in the breaking down of a portion of the wall of 
the oogonium and the formation there of a pore through which the 
sperms enter. Much slime is developed, which partially exudes 
from the opening. Numerous sperms are attracted to the oogonium, 
and one may frequently find conditions such as are shown in fig. 13, 
where the slime at the opening is filled with sperms held in the muci- 
laginous matrix. It is possible that such conditions were interpreted 
by Schmitz as nuclear material thrown off from the egg as a polar body. 
The union of the gamete nuclei takes place slowly. The male 
nucleus increases greatly in size, apparently being nourished in the 
dense central region of the egg, and the great increase in the amount 
of chromatin is as conspicuous here as in the female nucleus. Although 
the male nucleus is much smaller at first than the female, the two 
are approximately the same size before they begin to fuse (fig. 14), 
and both show essentially the same structure at that time. As fusion 
proceeds the two nuclei become indistinguishable (fig. 12). 
The history of oogenesis in Vaucheria may then be briefly described 
as from a multinucleate gametangium, by a process of rapid and 
complete degeneration of all the nuclei except one, which is reserved 
with all of the protoplasm for a single uninucleate egg. In these 
respects Vaucheria offers certain important differences and yet some 
fundamental points of agreement with the conditions in the Sapro- 
legniales and Peronosporales, which will now be considered. 
