252 Crithidia pidicis n. sp. 
9. The method of infection is contaminative, the post-flagellates in 
the faeces being the source of infection. There is no evidence of 
hereditary infection. 
10. Crithidia ly^licis is a member of the genus Crithidia, and is 
a true parasite of the insect, Pulex irritans. 
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Further references will be found at the ends of some of the papers quoted. 
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