STRUCTURE AND LIFE-HISTORY OF COPROMONAS SUBTILIS. 10] 
of ruptured cysts at this time which would suggest that a 
monad had emerged. All the cysts do not dissolve at the 
same time. I have sometimes, after carefully watching cysts 
on a slide which contained no free monads, found monads just 
liberated on another part of the slide at the end of the 
observation. After the cyst has dissolved the flagellum 
probably grows up from the basal granule, but this again I 
have not been able to watch. 
The cysts must reach the frog’s rectum by entering at the 
mouth and traversing the alimentary canal. They are 
probably ingested by the frog with its food, or in water, and 
must be very widely disseminated in nature, as they appear 
to be present in practically all frogs and toads. 
A similar kind of life is led by the shelled rhizopod 
Chlamydophrys stercorea, Cienk., whose life-history has 
been elucidated by Schaudinn (44). It lives in the feces of 
various animals, undergoing a remarkable development there. 
It is to be found sometimes in the feeces of frogs and toads, 
living side by side with Copromonas. Its presence here 
has not been previously recorded, I believe. 
Durable cysts of considerable thickness are formed by this 
organism, and it’ was proved by Schaudinn that it was 
necessary for these cysts to traverse the alimentary canal 
before they could develop in the excreta. Simply placing the 
cysts in the feeces does not suffice to open them. In Copro- 
monas, however, this is not the case. As long as the cysts 
are allowed to remain in the faeces for a day or two they can 
undergo development. It is not necessary to pass through 
the frog. This can be shown in the following manner: A 
small drop of an old culture which contains many cysts is 
allowed to dry on a coverslip. This kills any free monads 
which may be present, but does not injure the cysts. The 
contents of the large intestine of a frog are taken and diluted 
with water or salt-solution. This is then boiled for some 
minutes, in order to kill any organisms which may be present, 
filtered, and boiled again. The resulting liquid is quite free 
from monads, but forms an excellent culture medium for 
