237 
THE STRUCTURE AND LIFE HISTORY OF CRITHIDTA 
PULICIS, N. SP., PARASITIC IN THE ALIMENTARY 
TRACT OF THE HUMAN FLEA, PULEX IRRITANS. 
By ANNIE PORTER, D.Sc. Bond. 
Quick Laboratory, Cambridge, and University College, London. 
With Plate X. 
CONTENTS. 
PAGE 
Introduction.237 
Material and Methods ..238 
Distribution of Crithidia p^dicis in Pidex irritans . . . 239 
Movements. 239 
Morphology.240 
The Pre-flagellate Stage ....... 240 
The Flagellate Stage.241 
The Post-flagellate Stage.242 
Division.243 
Method of Infection.244 
Some Eemarks on Insect Flagellates, especially of the Genus 
Crithidia .244 
Summary .. 251 
Eeferences.. . 252 
Explanation of Plate ......... 253 
Introduction. 
Foe some years now much of my attention has been given to the 
investigation of various Flagellates parasitic in Invertebrates. These 
parasites were various Crithidia and Herpetomonads and the hosts have 
been chiefly Hemiptera and Diptera. During the last three years, I 
have conducted research on the endoparasites of the fleas found on the 
