Rhizophidium acuforme (Zopf) Fisch. 179 
gradually absorbed through the mycelium. Finally there is left 
of it nothing but a few reddish granules, of nearly the same colour 
as the eye-spot of the Chlamydomonas when it was in health. 
Towards the end of growth the thin wall of what has now 
become the zoosporangium of the Rhizophidium bulges out at the 
summit into a little papilla of mucus which is surrounded by a 
definite circular margin : the mucus evidently arises by the con¬ 
version of a determinate area of the cell-wall into a substance 
which swells up in water. There are by this time formed within 
the sporangium a number, 20-50, or it may be 50-80 (according to 
its size), of little rounded masses, each enclosing a minute oil- 
drop. These are the zoospores, which arise in the following way. 
At first, as has been said, only a few scattered oil-drops are seen 
in the clear protoplasm, these then increase in number, becoming 
smaller as they do so, and each is surrounded by a little mass of 
protoplasm which can be brought into distinct view by running in 
iodine solution. When these are mature, the papilla has reached 
its greattst size, and the zoospores begin to escape, a few at a 
time or more slowly one by one. The single flagellum trails behind 
and the oil-drop occupies the rear position. When the number of 
zoospores in a sporangium is reduced to a few, it is interesting to 
observe the remainder as they escape very slowly, often with an 
interval of several (15-20) minutes between each. Those left 
move freely about in a jumpy way, and one occasionally will 
thrust its head into the mass of mucus and push or wriggle in its 
efforts to get through: these may continue for several seconds and 
then succeed, or the zoospore may give up the attempt for a time 
and continue its wanderings within the sporangium, though it 
returns again and again persistently to the place of exit. On 
emerging the zoospore usually travels two or three times the 
length of the sporangium away, and then rests for a few moments 
before beginning to travel in a curvilinear course varied with a 
series of hops and skips. 
In the free state the zoospores can be seen threading their way 
among a mass of Chlamydomonads like a number of sight-seers pro¬ 
menading down Oxford Street and gazing into the shop windows 
on either side, or rather they are more like a crowd of farmers up 
from the country at a Cattle Show, passing irregularly from pen to 
pen and choosing which animal they shall buy. Similarly the 
zoospore seems to inspect the Chlamydomonads, as if selecting its 
victim. After it has fastened upon one no power is left to its 
prey to shake off the burden, though the Chlamydomonas still 
