152 Trow.- — Observations on the Biology and 
contents to be obtainable by any other method than one 
which involves sectioning. Let us proceed to the examina- 
tion of the actual facts revealed by the sections. 
The zoospore (Fig. 31 ). The zoospore as seen in section is 
generally of circular outline and clothed with a very delicate 
cell-wall. When the fixing has been properly carried out 
there is no collapse of the protoplasm, and the cell-wall is 
practically invisible in balsam-preparations. The protoplasm 
is finely granular and vacuolated and contains a few micro- 
somata of large size which stain deeply with nuclear stains 
and are in all respects like the similar structures already 
described by me in Saprolegnia. The nucleus is very large 
and spherical. It possesses a distinct nuclear membrane and 
what appears to be a central globular nucleolus with a spongy 
structure. This central body stains very deeply with nuclear 
stains, and appears to be kept in position by a number of fine 
threads which pass from projections on its outer surface to 
attach themselves to the nuclear membrane. The clear 
material through which the threads pass we may regard as 
nuclear sap or nucleo-hyaloplasm, the threads themselves as 
linin-threads, and the central body as containing both chro- 
matin and nucleolar matter. As we shall see later, it resembles 
in its behaviour during karyokinesis, the so-called nucleolus 
of Spirogyra ; indeed a close study of the work of Mitzkewitsch 
(’98), and especially of his careful figures, has revealed quite 
a number of points of agreement. We cannot then describe 
it either as a nucleolus, as has been done by Dangeard, or as 
chromatin, or a chromosome, as has been done by Humphrey, 
Hartog, and myself. 
The mycelium and sporangia. A study of the mycelium 
and its development from the germinating zoospores has 
revealed no fact of interest. The sporangia, however, are 
generally very large and contain both peripheral and central 
spores. In a transverse section we may find a central mass 
of four or more spores, occupying the place of the central 
cavity seen in sporangia of Saprolegnia , and surrounded by a 
parietal layer of spores. The spores frequently fail to escape, 
