Trow . — The Karyology of Saprolegnia . 625 
with dense protoplasm is the young sporangium. It becomes 
delimited from the mycelium by a cell-wall — the basal wall 
— and there is not the slightest doubt that the protoplasm at 
this stage contains the number of nuclei necessary to furnish 
each zoospore with a single nucleus. Fig. 3 a illustrates 
a transverse section of a fairly old sporangium with the 
zoospores nearly mature, and Fig. 3 b and c illustrate radial 
and tangential sections respectively of the lower portion of a 
younger sporangium. These figures will suffice to indicate how 
little need there is to dwell on the morphological characters. 
The nucleus, it will be noted, has again become spherical. In 
Fig. 3 a the zoospore-rudiments are almost separate ; they are 
connected together merely by very thin strips of protoplasm 
which ultimately get ruptured and so give rise to the spores. 
In Fig. 3 b and c the protoplasmic bridges, connecting the 
young spores, which have been so frequently described, are 
well seen. It may be worth while to note that the sections 
appear to prove conclusively, if this were any longer necessary, 
that there is here no possibility of the formation of a nuclear 
or cell-plate or special expulsive substance. I have examined 
with some care sections of younger and older sporangia, the 
latter with the zoospores fully formed ; but these furnish no 
additional features of interest. 
Development of the Oogonium up to the complete formation 
of the Oospheres. The development of the oogonium has been 
most successfully followed in .S'. mixta , but there is no reason 
to believe that the other forms do not agree with this one in 
every respect. When an oogonium is formed at the end of 
a hypha, the latter ceases to increase in length, but grows in 
breadth, so as to give rise to a more or less spherical head. 
Large quantities of protoplasm and numerous nuclei pass into 
it. Fig. 4 illustrates a median section of a young oogonium 
which at this stage contained seventy-two nuclei : it is to be 
noted that the vacuole of the hypha extends into the oogonium. 
A careful examination of the nuclei shows that their structure 
alters coincidently with their passage into the oogonium. In 
the hypha below the swelling the nuclei have the normal 
