626 Trow . — The Karyolovy of Saprolegnia. 
vegetative structure. In the swollen portion the chromosome 
has become irregular in shape, and the nucleo-hyaloplasm 
takes up stains readily. The chromosome, with the double 
stain used, becomes violet, and the nucleo-hyaloplasm a dull 
red. The nuclear wall is extremely well defined ; indeed the 
nuclei at this stage are very easy to demonstrate. 
When the oogonium has attained its full size, the antheridia 
come into contact with it, and the basal wall is then formed. 
Fig. 5 represents this stage, and shows clearly that the nuclei 
are still in the same condition as that shown in Fig. 4. The 
number of nuclei in this particular oogonium was very small, 
and they were also of unusually large size. At this stage, the 
oogonium may, as figured, have no central vacuole : in by far 
the largest number of cases, however, a central vacuole appears 
to be present ; and at all later stages up to the formation of 
the oospheres this is particularly evident. 
Soon after the basal wall is formed, the nuclei of the oogonia 
undergo great changes which are extremely difficult to follow 
except in excellent preparations. As these changes have 
been either overlooked or partially overlooked, and entirely 
misinterpreted by all previous observers, I must here devote 
special attention to them. Careful and detailed examination 
of the nuclei shows that the microsomata in the protoplasm 
bordering on the nuclear wall become more deeply stained 
and conspicuous. The chromosome- mass undergoes division 
into two generally more or less unequal parts, and this process 
appears to take place, as represented in Fig. 6 a , by the appear- 
ance of a large cavity in the spongy mass immediately under 
the surface, near to which, therefore, it is thus bordered by 
a thin membrane only. The thin part appears to be ruptured, 
and the splitting commenced in this way is continued until 
the chromosome has been divided into two rod-like halves. 
Fig. 6 b , c, d , and e is very instructive. In d the rods produced 
by the division are shown in plan, in e in profile. Fig. 7 
represents one of the sections of the oogonium from which 
these figures were drawn. 
Somewhat older oogonia show that the rods escape laterally 
