Trow . — The Karyology of Saprolegnia. 623 
In the centre of the nucleus is a spherical mass, which in 
deeply stained preparations appears homogeneous, and has, 
I believe, always been figured as such. This may be regarded 
as a chromosome. Dangeard looks upon it as a nucleolus. 
In good preparations its substance is seen to be distinctly 
spongy ; median optical sections, in particular, have the 
appearance of a network. The cavities of the meshes appear 
to be filled with a substance which has not the same affinity 
for nuclear stains as the substance which forms the boundaries 
of the meshes. Although it is a difficult matter to decide, 
I think that the strands of this meshwork never become 
resolved into threads or rods of any kind: it cannot conse- 
quently correspond to the nucleus of higher plants. The 
chromosome is apparently suspended in the middle of a 
nucleo- hyaloplasm — which occupies the space between it 
and the nuclear wall — by a number of threads, which are 
only distinguishable from the nucleo-hyaloplasm which they 
traverse, and of which they probably form a constituent part, 
by their reaction towards stains. It is frequently difficult to 
detect these threads, even in preparations which are otherwise 
good, and a detailed study of them has not been possible with 
the lenses at my disposal : they appear most clearly and 
constantly in the acetic carmine preparations. The zoospore 
generally contains a somewhat large vacuole. 
In the young zoospores, before germination begins, one 
finds in the best preparations a number of granules close 
underneath the external surface. Two of these are frequently 
elongated and arranged as if constituting a pair, and I have 
consequently been inclined to regard them as having some 
connexion with the cilia. They stain deeply with nuclear 
stains and are represented in Fig. 1 a , between the nucleus and 
the vacuole. 
Division of the Nucleus. Germination . Development and 
Structure of the Mycelium. Germinating zoospores frequently 
appear in the preparations, and it is by no means uncommon 
to find them conveniently sectioned in the plane of the germ- 
tube. The nucleus first undergoes division, and the division, 
