Herpetomonidae found in Scatophaga Hottentota. 63 
get infected through swallowing a fly containing Heiyetomonidae in its 
gut. It is usually admitted that flies infect each other by the contami- 
native or "casual" method, i.e. by ingesting faeces containing encysted 
protozoa of the Heiyetomonas group. The same is considered to hold 
good for similar parasites found in fleas and lice. 
Herpetomonidae have so far only been known to occur as harmless 
parasites in arthropods, and as pathogenic micro-organisms in mammals. 
Therefore the presence of these protozoa in Cliamaeleon ijumilus deserves 
some attention, for it may yet prove to be a biological transitional stage or 
condition. Cultural tests and animal experiments appear to show that 
the Leishmania bodies found in human beings suffering from kala-azar 
and Oriental sore and also in naturally infected dogs in Mediterranean 
countries are but resting stages or encysted forms of Herpetomonidae. 
In the present instance we may have been able to observe a more or 
less permanent stage in the cycle of evolution from the saprozoic existence 
in arthropods such as the fly and true parasitism in a warm-blooded 
animal, by adaptation to an apparently harmless residence in the cloaca of 
a cold-blooded vertebrate. 
