339 
on Saprolegnieae. 
The first stage I shall describe is the mastigopod swarmer, 
or zoospore, which may frequently be found in and about the 
infested hyphae of old cultures about 9 o’clock in the evening, 
or later. It is oblong (7-10 /x long), acute in front (Figs. 1, 2), 
with one or two anterior flagella, blunt behind or acute with 
posterior tractellum ; in this variability it resembles the type- 
species P. parasitica, as indeed in almost every respect. Each 
has a nucleus of the rhizopod or myxomycete type, i. e. vesi- 
cular with the nuclein in a spherical central mass ; and there 
is at least one contractile vacuole anterior to the nucleus. 
They swarm hither and thither in the hypha for a long time 
before escaping, and then swim about freely in all directions. 
Being usually formed in closed hyphae they must escape by 
boring through the wall by the emission of a pseudopodium, 
but the actual escape has eluded my observations. After a 
prolonged period of active swimming, less rapid and peculiar 
than that of Chytridian swarmers, they settle down on the 
walls of living hyphae, glide along them amoeba-fashion, and 
finally penetrate into them. I have not seen the full process 
of penetration ; but in several cases I have seen the amoeboids 
emit a long pseudopodium through the cell-wall and parietal 
protoplasmic investment of the living hypha and wave for 
some time in the lumen (Figs. 7, 8). We can scarcely doubt 
but that the rest of the body follows suit after the fashion of 
a white blood-corpuscle in diapedesis, but, of course, inversely. 
The aperture must be elastic and closes completely, possibly 
by secretion of cellulose from the fungal protoplasm ; for there 
is no loss of turgescence in the hypha so attacked. The stage 
we are at now is usually termed ‘ amoeboid’; but ‘ HeliozooicL' 
would be the better term, since the pseudopodia are always 
radiate and stiffish, as in most of the Monadineae. 
The amoeboids may exist in large quantities in the hyphae, 
probably from simultaneous or consecutive attacks of numerous 
swarmers. Without denying the possibility of multiplication 
by fission in this stage (as occurs in P. parasitica, according to 
Zopf) I must state that I have never seen any indications of 
it. From the figures (4-8) may be seen the very characteristic 
