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THE MORPHOLOGY AND LIFE-HISTORY OF CRITHIDIA 
GERRIDIS, AS FOUND IN THE BRITISH WATER-BUG, 
GERRIS PALUDUM. 
By ANNIE PORTER, B.Sc. Lond. 
(With Plate IV.) 
CONTENTS. 
Introduction ..... 
Material and methods 
Occurrence of the Parasite in the host 
General Description .... 
Movements ..... 
Morphology ..... 
The Pre-flagellate stage . 
The Flagellate ,, 
The Post-flagellate ,, 
Division ...... 
Mode of infection .... 
General remarks .... 
Summary ...... 
References ..... 
Explanation of plate 
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Introduction. 
One of the most noteworthy advances made in medicine in recent 
times is the recognition of the part played by insects and other 
Arthropoda in the spread of disease. It is only necessary to recall the 
connexion of malaria with mosquitoes, of human relapsing fevers with 
Ornitliodoros moubata, and of sleeping sickness with the tse-tse fly, to 
recognise the enormous importance of the economic side of protozoology 
in connection with Arthro'poda. 
