222 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
oogonium these patches are sharper and better differentiated, but 
traces of them can be seen here. The history of these fine meshed 
patches and the sharply differentiated mass which they finally pro¬ 
duce, was followed in some detail and it seems better to discuss it 
in another portion of the paper. It will be sufficient at this time to 
call attention to its manner of origin as cytoplasmic patches at the 
time the peripheral vacuoles are enlarging. In the meantime, the 
intervacuolar strands, which are in reality not strands but sheets of 
t/ 
cytoplasm, have become fine meshed and appear dense and granular. 
In form the vacuoles are now roughly hemispherical with their plain 
surfaces turned outward and parallel with the oogonial wall (pi. 12, 
figs. 11 and 14). 
As these changes take place in the intervacuolar strands, there 
appear the first evidences of a differentiation in the region w T here 
periplasm and ooplasm are later to be separated. This simultane¬ 
ous differentiation of the intervacuolar strands and the region sep¬ 
arating periplasm and ooplasm continues until the oogonium reaches 
the condition represented in figure 16 (plate 12) where the differ¬ 
entiation is complete and the oospore practically mature. 
In the meantime, the nuclei have, in all probability, divided once 
mitotically. The writer did not succeed in finding stages that 
showed this point with absolute certainty but such a condition as is 
represented in figure 15 (plate 12) undoubtedly suggests a simulta¬ 
neous mitosis of all oogonial nuclei. It should be distinctly stated, 
however, that this stage in Araiospora is by no means as conspicu¬ 
ous nor as commonly met with as is the corresponding one certain, in 
species of Albugo. Sufficient evidence was found, however, to indi¬ 
cate that in all probability such a division occurs here. It will be 
seen that the long axes of the nuclei in figure 15 (plate 12) are 
turned in various directions. Those on the left show a few deeply 
staining bodies that are probably chromosomes. On the extreme 
lower side of this figure is a dividing nucleus so situated that one 
daughter nucleus could be cut off with the oosphere and the other 
with the periplasm. 
The central ooplasm and oosphere .— Soon after the oogonium is 
cut off, and even before in some cases, the cytoplasm of the oogo¬ 
nium forms a more or less regular, coarse mesh work. At this time 
the thirty-five of more nuclei of the mature oogonium have moved 
out near the periphery. As they take this position, incipient stages 
