An Investigation of a Species of Saprolegnia. 313 
just one minute, that is from the appearance of the small bud to 
the time when the zoospore had completely discharged. The 
zoospore now remains attached to its empty case for a period 
varying from four to ten minutes, or in some cases half-an-hour. 
Just after leaving the case the zoospore is nearly spherical in form, 
the first change noticed is a slight elongation in a direction 
tangential to the empty cyst. A contractile vacuole appears, and 
the cilia are seen as outgrowths, but their point of attachment is 
very indefinite, as they seem to wrap themselves round the spore 
and keep up continuous undulating movements. Their growth in 
length tfnd the increase in rapidity of their motions is distinctly 
noticeable. When the cilia have developed to a certain length, 
their motion in the liquid medium causes the whole zoospore to 
rock, while attached to the empty case. As the cilia attain their 
full size the rocking motion increases, and suddenly the zoospore 
becomes detached, and swims rapidly away. The second motile 
stage lasts much longer than the first—usually from twelve to 
twenty-four hours. The spores then come to rest, and develop a 
cell wall, and usually commence to germinate directly by putting 
out a germ tube, which, in a suitable medium, can produce a new 
mycelium. 
A difference in the forms of the two kinds of zoospores was 
noticed and also the motion in the water appears different—that of 
the second form being much more active. The following method 
was used for examining them in detail. A hanging drop culture 
which was seen to possess many zoospores was taken and from this 
some of the water was removed with a platinum loop to a clean 
slide, a small drop of water was added and the whole slide then 
inverted over strong glacial acetic acid for thirty seconds. A trace 
of chlor-zinc-iodine was added and a cover-glass placed on the 
drop. This method stains the cilia well; the point of attachment 
can be seen to be terminal in zoospores discharged from the sporo- 
cyst (Fig. 34), but in the case of those of the second motile stage 
the point of attachment is very difficult to make out. In many cases 
in the second stage a difference in length between the cilia was 
apparent, whereas in those of the first stage the cilia are equal in 
length. The zoospores of the second stage (Fig. 35) seem to be 
less sharply pointed than those of the first and to have a clear 
central vacuole as distinct from the smaller apical vacuoles of the 
zoospores of the first stage. 
After discharge of the zoospores, the end of the hypha was 
