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found on the same individual. After attaching itself to its victim, 
the zoospore surrounds itself with a membrane, pierces the thin 
cell-wall of its host, and sends a short and slender mycelial tube 
through it into the cell; this tube often enlarges slightly just 
below the puncture to form an appressorium which holds it 
securely to the prey. The tube then grows further and sends out 
a few short stoutish branches which spread over the surface of the 
protoplast and act as haustoria ; no threads could be detected 
within the protoplast. 
Fig. 1. RHIZOPHIDIUM ACUFORME ON CHLAMYDOMONAS. 
a. The Chlamydomonas in health. 
b. The Chlamydomonas with a zoosporangium as large as itself attached. 
c. Formation of the beak and oil-globules. 
d. Formation of zoospores. 
e. Escape of the zoospores. 
f. A Chlamydomonas with two empty zoosporangia, 
g. Another with three sporangia full of zoospores. 
h. With a young zoospore just attached, plasmolysed with iodine. 
i. Showing the mycelium with branched haustoria, attached to the 
protoplast. 
k. An evacuated sporangium, containing one dead zoospore, and showing 
the curled back edges of the pore. (All magnified 1000 times.) 
At first the zoospore is rather less than 2 /* in diameter, 
and oval or nearly round in shape ; it grows rapidly, remaining 
the while all but spherical, until if there is only one on the 
Chlamydomonas it becomes as large as its host, i.e., it may reach 
a diameter of about 15-16 ft, the host measuring on the average 
20x12 jx. During growth it is filled with a clear colourless pro¬ 
toplasm, which can only be seen by plasmolysing: in this are 
often embedded a few (1-6) relatively large round oil-guttules. 
Meanwhile the protoplasm of the Chlamydomonas has withdrawn 
from its wall and collected into an irregular mass which is being 
